Well, one simple thing we could try to possibly rule out some font issues is rebuild the font cache:
sudo fc-cache -fv
Personally, Iād also be interested in the output of the following:
cat /proc/meminfo
and
cat /proc/swaps
It might even be related to swap issues. The kernel swapping relevant data away and the swap somehow having been corrupted when the data is addressed and needs to be retrieved from swap. Lots of options where things could be going wrong. 
But, never give up, never surrender!