I think I've been having similar problem. Started after the latest update here as well. The whole webUI goes unresponsive, iowait times go high as hell. Going to commandline to see some system details, most of the times the commands just hang and I can't even CTRL-C out. The system did that just a moment ago, had to force shutdown and I'm now doing parity check.
I was thinking it could be a bottleneck from slow HDD's and things like finished downloads overloading the transfer capacity? I started to at the Docker containers, but could not find any clues if they are the root of this problem. What containers do you have enabled and are in use? Does anyone have any good tips where to look when trying to find the cause for high iowait?
I found this discussion from Docker Github, could it be related to this one? They seem to have concluded it to be a kernel bug.