I am experiencing the same isssue with my FP6 since I had the bad idea to upgrade from 3.7.3 to 4.2 official yesterday. BoursoBank worked in 3.7.3 with Shelter workaround.
I tried several configurations after a factory reset in 4.2.
- install BoursoBank from AppLoundge and tick the app in Système \ Compatibilité de applications \ Masquer aux applications. I tried in Anonymous and with Google account in AppLoundge. This was added to simulate the workaround but it doesn’t work, at least for us.
- the previous Shelter workaround doesn’t work with 4.2.
I always get the following message.
I will have to restart my previous Android phone only to use from time to time BoursoBank 
I hope @AudeM will provide such a trick to mitigate this issue 