Nearly three years later I am facing the same problem, was there no solution/bugfix in the meantime?? When i try to upload for example 45 pictures from my Galaxy S9 to Boxcryptor, it succeeds for only 30 pictures, the rest fails with "upload failed". When i try it again, it succeeds with maybe 10 pictures more, so that i have to try it several times to get all 45 pictures uploaded.
I tried the same with other pictures on another phone (Galaxy S10), but the problem was the same.
With this bug, Boxcryptor is unusable!?
Any idea how to solve this problem?