Kind of surprised no one else brought this up, but I get these warning popups:

Message: Error loading Interface\AddOns\EventHorizon_Configs\core_my_config.lua
Time: Thu Jul 19 22:57:28 2018
Count: 3

I don't use the myconfig features, so removing the offending lines from the toc files fixed it for me.

We've been chatting about it on Discord. It seems that Blizzard has changed it so it pops up warnings for files missing from the toc file, the old behaviour didn't do this.
It works fine but the warning is irritating.

Interestingly it didn't do this on the PTR or the Beta.