Android 6 already had painful mediaserver glitches that drained the entire battery in less than 1 hour.
Android 7 has a new glitch: (Next to crippling USB-OTG access for ridiculous security excuses, )[Android 7 Nougat onwards: hides USB OTG sticks from third-party file managers?, the otherways smooth and highly responsive system gets so slow while copying files, even unable to compete with an antique computer that has been upgraded from Windows 2000 to Windows Vista - Service Pack 0.
I also sometimes get stuck on black screens, sometimes it refuses to wake up from stand-by and it also gets stuck on a homescreen without icons (only wallpaper), until the exact moment I pull the USB stick.
It even once rebooted.
USB-OTG is something where even mobile phones from 2011 outperform those from 2017, 2018 and 2019 in terms of usability and functionality.
The same glitch also cripples data transfer to other flash drives as well, which means the problem is not specific to the flash drive.
Edit 1: The folder the files were moved from is excluded from the media scanner using