The other day I was getting this weird little error when building a canvas app. Basically, all of my CDS Optionsets just randomly stopped working.
I hadn’t actually realised that I had left the “Experimental Connector” setting on while testing out the lookups. I think there must have been some sort of update. Pop into File | App Settings | Advanced Settings and turn of that little toggle.
I hope this helps someone out because I had a mild panic 😉