Have you considered not trying to force ttyUSB0 but instead creating a symlink to whatever tty is assigned? Your software then just uses the symlink.
A problem with forcing a particular tty is what if you boot without the Arduino but another device is attached? You then need to convince the other device to skip ttyUSB0.
If you would consider a symlink then ...
The fact that you're referencing ttyUSB0 tells me you have cheap Chinese clones and not genuine Ardunios. These are usually based around the CH340 USB interface chip which is notoriously unreliable.
Your UNO is dead.
My supposition is that plugging it in cripples the CH340 driver. Any other boards that you subsequently plug in can not be recognised because ...
sudo usermod -a -G dialout $USER
cleared the issue it was the first time I have used that machine with an Aduino not sure how it was running before with out permissions set up correctly or why it failed when I dropped that 5v, I assume that just reset the board and when it tried to reconnect it failed. Both board and PC all working fine, phew.