When I installed your application and tried to search for BT devices, it generated an error due to lack of permissions, but after granting them, it worked well!!
Later on, I reset the permissions for my applications, and they started working again. I really don't know why it worked now and not before since I had already checked the permissions. I suppose I must have done something else but I don,t know what!.
On the other hand, my applications still don't work properly on a GT-N511 tablet with an older Android 4.4.2 system, even though permissions have been granted. It's a complete mystery. Anyway, thank you very much for your help.