@ Morning wood & Nemethmik:
you should not worry, I have indeed contacted Andreas Rogge to get his expert opinion. As mentioned in my initial post:I really love the sound of my A. Rogge chanter and it is well and precisely tuned.
If not clear enough this means that although I find it difficult to play I have no doubt about its highest quality, also explaining why after cautious considerations I have decided earlier this year to order this chanter to Andreas. If I had to make this decision again I’m 100% positive that I would order a chanter to him. And when I will have succeeded to master this chanter well enough I will order my half set to him.
I’ve also mentionned in my first post that although I’m not a total beginner, I do not consider myself as a skilled piper. Meaning that although I suspect a reed issue most probably linked to the specific climatic conditions of the Côte d’Azur/french Riviera, I also certainly do not exclude the possibility that moving to a high quality chanter could be an additional reason for my current problems. I was thinking that some other pipers may have experienced this in their “young piper years” with a Rogge chanter and would share their views.
Now I have learned from both your posts that I’d better wait for the next 10 years or so to become a fully skilled piper before daring to post “silly” questions.
This is not the idea I had about forums. Iwas silly enough to think these were dedicated to allow musicians to exchange in an humble manner on their respective experiences, beginners gaining precious advices from more experienced ones etc. This is obvioulsly not your point of view.
@ all others :
Many thanks for your very helpful and supportive answers. To summarize here are some answers to your questions:
it would be unusual to have to season the bag if it is new (is it one from Rogge or from someone else?
Bag and bellows are from another make -now I’m more cautious about mentioning names, sorry… 
a bag playing a very light set up might also start to leak when a higher pressure is required for a stiffer reed)
It is true that I have considered changing the belows for Andreas production -but this was additional money to spend… suspecting that these were maybe well adapted for another type/first chanter but maybe not for this new one.
I also maybe have to mention that these belows had a very thick and hard leather on which I’ve sweated a lot when I’ve started playing, on top of normal sweating on belows for a beginner.
Once Peter Browne came to give a UPs master class at the Festival Interceltique de Lorient, I went to discuss this particular point with him and he recognized that my bellows leather was particularly hard, showed me his for comparison, saying he never experienced my problem but had no precise advice to help softening it. Since then, over the last 2 years the leather has gradually softened while I was playing and playing and playing… yet I must admit it remains harder than most of the belows I have been able to see here and there. My UP teacher also noticed it but never actually tried them as they do not fit her waist.
-it would be very strange to have not one but two leaky new reeds …I presume the problem is happening with both reeds?
It is more pronounced with one of the 2 reeds and while double checking I’ve noticed that the worst one is less open. So here is probably the answer… 
-how did the set play on the first day or so after you received it?
-has it changed since then?
Well… didn’t want to mention this before… I’ve received my set in July while I was in the hospital due to unexpected illness. When I was back home I had to wait for some weeks before being able to try it- was a real torture to look at this gorgeous chanter without being able to play it
!
I’ve tried it as soon as possible before sending a thank-you mail to Andreas, explaining why I had not been back to him earlier and telling him that I already had pbs to play the low notes but was thinking this was due to my physical conditions. Had to wait until Sept. to be able to fully recover with my bellows arm. At that time I was spending some time in Brittany (where most french pipers are located) so went to see a pipe maker down there to get his opinion => was it me or a reed pb… or both ?
He’s kindly spent 30 minutes trying it with his bellows & bag, my reed on my chanter or one of his, got the same result with my reed + chanter, tried one of what he called his best reed on my chanter, found out that it was a bit better although he clearly noticed that my chanter was much more difficult to “control” than one of his and that my reed was definitly not permissive in terms of switching from high to low octave or simply to get the low D (=> diagnosis in french was “anche qui octavie très très facilement !”), made me try all this by my own (with my own belows & chanter) looking & listening to me playing, looked more closely to the inside of my chanter and removed a “few dirts” then concluded that yes, it would take some time to master this chanter.
-you don’t say how the upper octave is playing for you
that info would be helpful too
The high octave is perfect so far. The pb being really that the low octave does not come naturally but instead the high notes come in the first instance. I pay specific attention not to throw too much air into the chanter, but when I have the bag full and I relase the pression on it and stop the bellows I should be able to get the low D right away. Correct me if I’m wrong but an easy and stable low D is essential, right ? Well, it is essential to get all notes, OK
… but one should - after 2 years playing, be able to get this fairly easily !
So, when playing series of high octave notes then trying to go back to low notes is a real pain. I either get high notes or a mute chanter. As an example I often play Sean Bhui followed by Ward’s jig and find it easy to play the 1st tune but when switching to the second which is technically easier, it turns out to be a real pain => switching from high to low notes is nearly impossible with one reed and very difficult with the second one.
There are a few UP players in the South of France e.g. Toulon, Marseilles and also near St Tropez so it would be good if you could make contact with one of these as they may be able to correct the problem. Jerome in Marseilles also does lessons and will see if I can find his contact details
You can really count pipers located in this area on one single hand… however I’ve met a few located in Marseille, far more experiences than me, but I’ve never met Gilles. I hope I can drive to Marseille towards end of Nov to attend a session. We do not have sessions anymore in the Nice area. This may hopefully change soon, my whistle teacher is working on trying to re-start them…
My UP teacher is located in Marseille (Veronique), 2 hours drive/one way from Antibes. Since I’m currently on a chemotherapy it is not really serious to drive 4 hours in a single day and I’m unfortunaty even more isolated. But after mid-November when my treatment is over I’ll be able to commute again.
I’ve recently had an e-mail exchange with a piper located next to Antibes but lost contact. Hope he will answer my last mail as I do not have any other contact ingo on him…
However, thanks for the link, Chris, I will contact Marc Ruvini to get more info on pipers located in the Region Provence Alpes Côte d’Azur.
In conclusion: as soon as I will be able to travel again I will join a UPs & reed making workshop in Brittany and/or Ireland. I must admit that fiddling with my proper reeds (from reed makers !) makes me very nervous as I know that if I spoil them then I’m stuck for weeks. For the time being I will now follow some of the instrcutions Andreas gave me since I’ve sent my initial post and will keep in mind all your positive remarks.
And I’ll try to go back to reed making although, being fully conscious that one can hardly pretend to be a solid piper without knowing how to deal with reeds. And learning how to make reeds with the NP Dublin DVD + info collected on the web still represents a great challenge.
Let’s say that I kill pieces of cane one after another (at least it is relatively easy to buy some at reasonable cost down here!) and I add up questions to be asked when I ultimatly join one of these workshops… will most probably be a very demanding trainee ! 
cheers !