For the pendrive, did you enabled the OTG storage?
You will find that under settings
Press and hold the gmail app
Click on app info
Set it to don't optimise
Force stop the app and restart your phone once and see if it...
Hey @Vartika_Pandey_ they added 9 series in the list
If you minimise the YouTube app it play for few seconds but not after pause.
BTW press and hold the YouTube app