If Sai’s fix above does not fix, i.e. the initials are there, I think this may be a bug that I’ve seen before (assuming the resource is really assigned, just missing from the Gantt bar view. I remember the fix, albeit not good, was to delete the resource and re-add and re-assign it.
Btw, are you using Project 2019? I am, but my version is 1902 (Build 11328.202222) which I thought was the latest. Thx.