Weird white space in admin area

I have had this weird whitespace appear multiple times on multiple sites. By "appear" I mean, it wasn’t there one day, then it was. I am the only admin on these sites, which are in the cloud. I suspect some kind of infection, but I can’t figure it out. This image is from a blank site, Google cloud [happening on AWS also], fresh database, no plugins:

My previous solution was to reload these sites from Duplicator backups. That seams to have worked. This image is from a new DB and no plugins, so it must be in the core code on these sites. Since it’s happening repeatedly to me, I’d like to track it down.

Does anyone know what could cause this whitespace?