@Tokylabs, no, unfortunately i could never find what the problem was. i had some conversations with @BlynkAndroidDev and @vshymanskyy about these issues, but they said that bluetooth devices were working fine on their test. based on the debug log files and other information i sent from my phones they could not identify the problems i had.
this was several months ago, and in the meantime i had to advance with my project, so i had to find another solution for communication. i switched to wemos d1 mini pro, and using wifi.
however, it seems that after all this is not an isolated case, because i talked with other members on the forum, and they reported very similar problems:
and right now also @Tokylabs and @Gunner experiencing very similar problems…