@cowontherun - I know exactly what you’re talking about. Where a plugin is supposed to appear, it instead displays fallback text (ie. a cart icon shows the word “cart” in large serif letters).
(@keith, to fill in the gap, Bubble created a plugin that lets you pull from Google’s Material Icons instead of using the standard icon library).
While I don’t have a definitive answer, it seems to happen most on cruddy internet connections. (Ie. I’m using a mobile device on a commuter train). It usually fixes itself within a few seconds. But I’ve had a couple occasions where it stayed with the fallback text). If I’m able to reproduce, I’ll share.