Removable drive connected over OTG disconnects when screen turns off
Check if you have any option in Settings (maybe Settings-&gt;Storage) to keep OTG connected in sleep mode.
If you don't find anything related to that, it means there's some bug with the ROM.
Maybe you can try this app: USB Autosleeper
This app doesn't allow the phone to sleep when USB is connected.
Whenever you connect OTG, run that app and do whatever you want :)