I was experiencing various conflict errors with the auto upload function in NC Android app since quite some time already. Basically, every new photo or video was not uploaded form my phone. In the log files I did not find anything related.
My photos, etc. are organized in sub folders according to the settings of the Android app. When I was creating the folder 2020/10 on my desktop computer all the files could be upload again. That solved the issue for me … at least for this month 
Developer infos:
NC Android: 3.13.1
NC Linux: 3.0.2 (Ubuntu)
NC server: 19.0.4