Nothing wrong with my earlier post - I can see it clearly above your recent reply. Must be a glitch...
There's definitely something fishy about some associated user library component being updated or getting corrupted, because the system and applications are running flawlessly in another relatively clean user account on my Mac. Of course, it will turn out to be some freaky combination of an innocently appearing plist, log, or cache file. Wanna bet ?
Unfortunately I don't have enough time the coming weeks to try ruling out all kinds of possible causes in my simple user-centric fashion. I'm on a deadline every week for the next 2 months, so I really need my system to be rock solid. After that, I'll probably upgrade to Mojave anyway. Oh yes, there are always some bug reports and troubled situations with the latest OS version. But I don't worry too much about those. At least these newer systems and applications get all the attention and timely updates – which is much more than this old Sierra dog is getting from Apple...