I have a very odd issue with my external USB3 hard drive. Sometimes, I can use it with no problems, but sometimes it slows down the entire computer and freezes processes.
For example, spotlight might stop working, and if I kill it through the Terminal, no new spotlight process launches. And for example the dock might freeze, not responding to anything and just showing a beach ball when I put my mouse on it. Same thing with Finder.
Some things still work but the more I use the computer with the hard drive in, the more processes freeze, for example if I quit Safari I can't open it again. However, if I just unplug the cable suddenly every single process starts responding/working again instantly, with no problems.
I have tried to repair my hard drive through Disk Utility, but it finds no problems.