SSD filling up for no reason and crashing
I'm running High Sierra on a 2009 Mac Pro. My system disk is a 1TB SSD. I normally have it about 75% full.
I noticed it was surprisingly almost full so I did some spring cleaning and emptied the trash. I must have cleared about 250GB. The drive still showed with only around 45GB available though.
What's even more troubling though is that I've noticed the available space dropping incrementally over time. For example, this morning it was around 40GB available and 3 hours or so later that's dropped to 37.74GB.
What's making things even harder is that every time I try to "manage" storage to see what's going on, the computer will inevitably crash after a short while.
I can see that "System" is taking up 307GB which seems overly large but I'm not sure exactly what to do about it.
I tried running Omni Disk Sweeper but once it gets to about 187GB through, again the computer crashes.
It seems to be working fairly normally otherwise (if a little slow) and doesn't crash using other applications. I've also run a scan with Malwarebytes but no problems showing.
Can anybody offer any suggestions for next steps?
Mac Pro, macOS 10.13