Hi wojpen and k1w1_123,

based on your replies, I did two things:

1) put .fbl maps into "Maps" folder on tablet
2) modified sys.txt to reflect the name of SDCard - as I read in some articles on Internet, Android 6.0.1 uses card UID in the name of path, so it is /storage/9026-EFF8 on my device, so I modified sys.txt to this:

[folders]
linked_root_list="/storage/9026-EFF8"

To be honest I do not know which one option actually helped or if both were necessary, but currently
the application works perfectly. Thanks a lot for your help and naturally for upload !!!

Regards,

Majq