[SOLVED] CentOS 7 GUI freezes erratically

I've been noticing a problem in CentOS 7 that didn't happen to me under 6. As I upgrade the machines in my area from 6 to 7 (full wipe/re-install/recopy data. No in-place upgrade), I find that the gui unpredictably freezes at times. Usually I'm left with mouse control, but that's it. Clicks do nothing. The machine isn't totally frozen because if I do an ALT-F2 to a text console, I can log in fine. Don't see any large process taking up the cpu. But the Desktop is still frozen. I can also ssh in from a neighboring machine fine. But the only way to regain graphical control of the GNOME environment is to reboot.

Occasionally something like ALT-F1 to bring up the Application menu will give the GUI a "jump start" and control comes back, but not always. Less often than not.

Haven't been able to reliably replicate this either. Sometimes it happens almost immediately after login, once I've launched my first program (typically the Terminal or Firefox for me). But after a reboot if I do the same thing, no problem. Sometimes I can be working fine for a while and then I get hit.

All my machines are various models of Dells with assorted vintages of NVIDIA graphics cards. Most of them I have the right current proprietary NVIDIA driver installed, though a couple I left with the default Nouveau driver, where graphics performance isn't crucial. Doesn't matter. This problem happens either way.

Is this CentOS 7 problem familiar to anyone? And did you solve it?

Alternatively, is there a way to mitigate the problem by restarting the desktop only, leaving open programs (Firefox, etc) intact (similar to the way that bringing up the Application menu sometimes does)?

Have you checked the /var/log/Xorg.*.log files for errors?

I did not see any recognizable errors, but the next time this happens I'll check immediately and see if there's anything in that log happening in the moment. /var/log/messages never has anything that I recognize as relevant either, but I'll do the same in the moment next time and post excerpts.

So I guess this isn't an issue anyone else is encountering.

Since this post, CentOS/RHEL 7.7 has come out and as I've been updating from 7.6, I haven't seen the issue again. It's always hard knowing if a random issue is actually gone, but I'm feeling that this is fixed so I'm marking it resolved.