I'm working on a 21.5 inch late 2015 image, 2.8 with 8GB using Mojave. I'm not quite sure what steps are happening and if there is a hardware issue on my side, but when I use Illustrator, there is an intermittent bug that seems to happen. Here's how it goes:

Using Illustrator, usually the pen tool.
The spinning beach ball pops up.
The screen freezes for a few seconds.
When it pops back into play, none of the menus have text. Literally, NONE, even those outside of Illustrator (Chrome, the Apple drop downs to restart/shut down)

Is it just destroying my RAM or is it a bug that's suddenly emerged?