Run DriveDx (free trial period) to check the health of the hard drive. Post the complete DriveDx text report here using the "Additional Text" icon which looks like a piece of paper on the forum editing toolbar. While the overall HD performance was good in the EtreCheck report, there is a possibility some sectors could be starting to fail and were not being accessed during the EtreCheck performance check.
You should also run Disk Utility First Aid on the hidden Container. Within Disk Utility you may need to click "View" and select "Show All Devices" before the hidden Container appears on the left pane of Disk Utility. Even if
First Aid says everything is "Ok", click "Show Details" and scroll back through the report to see if any unfixed errors are listed. If there are errors, then run First Aid again until they are gone. If they cannot be repaired, then you may need to run First Aid while booted into Recovery Mode.
Disconnect all external devices from the computer (except keyboard & mouse of course) in case one of them is causing a problem.
Try booting into Safe Mode to see if that makes any difference.
You may also want to run the Apple Diagnostics to see if any hardware issues are detected.