What's up with Gedit's HTML highlighting?

I've been learning some HTML code recently, and something weird is up with Gedit's highlighting. Whenever I try to use the <h3> tag, Gedit immediately cancels all the highlighting and the text becomes plain white. If I leave and come back, the problem persists. The only way to get the highlighting back is to restore and earlier version of the file by not saving or to start all over again. Does anyone know what's going on?

Extra details:

OS: Ubuntu 20.04

Gedit Version: 3.36.2

Gedit Color Scheme: Cobalt

Screenshots:

Pre-pressing enter (look at the tag)

Post-pressing enter