CSS crashing after any theme changes

Nextcloud 14
CentOS 7
PHP 7.2

Whenever I make any changes in the Themeing section and click my mouse, the preview only sometimes loads. Whether it loads or not, if I refresh my page or go back to my main site, it looks as if the site’s CSS is completely broken and all I see is black and white text all scrambled. The only way to fix this is with an Apache restart.