Yes, probably lucky.
The key difference in 4.0.0-rc23 had to do with handling symbolic Font Awesome version values like “5.x” or “6.x”, which we started using with the roll out of Font Awesome 6.0.0-beta1. Since then, new kits that are created default to version 6.x if your account has beta features enabled, or otherwise, they default to 5.x. You can also lock it to a specific version, like 5.15.3 or 6.0.0-beta1. Previously, this plugin had some validation rules that would have rejected a version option like “5.x”. rc23 now handles those versions appropriately.
So, it’s not really “lucky”, per se, but if you are using a kit without one of those symbolic versions, then you may not have stepped on this particular landmine. Or if you are running with the Use CDN option, you may not have stepped on this landmine.
At least, that’s my educated guess as to what factors would likely be involved in whether one experienced a fatal error in multi-site mode recently.
In fact, at one point, I almost wrote up some documentation to explain how to make it work in multi-site mode, even though it isn’t really designed for that–because it can work in some scenarios. In the end though, it felt too messy and confusing; I didn’t want to invite others into such chaos. So it seems better to just say “not supported” at this time.
I’m curious, @stv11c, whether you’re configured to use a kit or CDN and what version.