[CentOS] Perhaps trivial problem but important to me

I have two computers: CentOS 7 (KDE 4) and CentOS 8 (KDE 5). I'm also an avid Doom player (yeah, I'm an old geezer). On C7 using prboom v 2.5.0 and a graphical interface I wrote to select a wad file to play without using the command line, everything works fine. On C8, using the same prboom 2.5.0, graphical interface, and the same SDL libraries, the video is "jerky" - every 2 seconds or so the video stops for a fraction of a second and then restarts. This makes game play a bit irritating.

This problem does not occur when playing videos with mplayer, also using a graphical interface I wrote to select files to play.

I've looked at system settings, checked process usage using ps and can find no reason why there is a difference between playing Doom in C7 and C8.

Any suggestions will be greatly appreciated.

Jeff