Back in ArcMap I had an issue with a curve doing some pretty chaotic things. I finally found what was causing my issue and it was a historical parcel. The biggest catch was it was a historical parcel I couldnt see. I had to change the Query for the historical layer to show EVERY historical layer regardless of type. I found something I had used to sketch a shape deleted it and after that the curve worked. It was bizarre.
Hi Anne, this problem has been reported previously, and was fixed in 10.6.1. (Reference: BUG-000099453) If you are already at 10.6.1 or higher, then please respond here to let us know. Otherwise if you are working on a release earlier than 10.6.1, there is possibly a workaround, but I'd need to research it further before providing the steps, and I may also need your data as well to confirm it's the same issue and to confirm that the workaround is valid.
I'll message you so we can figure out next steps.