[taxcontrol]

Sounds like you need to alter your X11 config file and force 60Mhz or force your monitor.

Possible hints to fix:
https://forums.linuxmint.com/viewtopic.php?t=203112

https://www.reddit.com/r/linux/comments/7w4tnv/how_i_got_my_4k_monitor_working_at_60hz_in_linux/

https://delightlylinux.wordpress.com/2017/09/15/how-to-set-the-default-monitor-refresh-rate/

[zeugma]

Thanks for the links. They gave me some ideas to try tonight. There doesn't seem to be an xorg.conf file anywhere under /etc, so I'll likely be rolling my own. The biggest problem with testing this, is I have to wait quite a while after making a change for the problem to recur. If I just logout and log back in, it doesn't happen.