Hey!
I can't believe this bug is back once again... I've been using 2017.1 myself so maybe it's something with 2017.3...?
You're right in the cause of it, it's caused whenever the font atlas gets updated, but STM doesn't rebuild for some reason. STM is subscribed to an event that gets invoked to call Rebuild() whenever its font atlas updates, but for some reason it doesn't always call Rebuild()...? I thought I fixed this 100% before, but I've learned a lot about events in the past few months, so I'll revisit that code and see if it's something to do with that. I am curious if it has something to do with that name box having bolded text, though.
In the meantime, you can avoid font atlas updates altogether if you set your game's font to be non-dymanic. (Go into your font's import settings and change that there) The only downside to non-dynamic fonts is that you can't adjust their quality, and they dont do bold/italics. You can change this in the font's import settings.
I'll look into this again shortly, sorry for the inconvenience!