Font display breaking

Hi All

It seems after almost 2 months trouble free my font display problem is back. In the image below you can see that some of the fonts appear corrupted and some don't display. If you look at the 2 spreadsheets side by side, you can see that the same text in the same font behaves differently in the 2 different files. Some programs seem unaffected, and others heavily affected. Chrome and Firefox have no issues at all.

Everything appears fine after a reboot, and the problem only starts after the 1st time the desktop has to be unlocked.

Any help with diagnosing the problem would be great. Last time I just reinstalled and it went away, but I am not excited about doing that every 2 months. Reboots are also a pain.

Thanks in advance.