error finishing read

OK, that might be several things, so check the "processes" tab when that happens, see what is causing such CPU usage.
Another thing that can do such high usage is file system journaling, especially if the hard drive is on its way out.
Disable automatic updates, i do that always, also disable everything you do not need from the "startup applications" in "preferences" menu.
This can also happen at random if there is a broken PDF file somewhere on the drive, very hard to pinpoint, had this issue several times. Easiest way to find this out when opening file browser if the thumbnails take long to show or do not show at all for some file types.
And yes, these are all for Linux Mint, although other distros can have the same issues.