Hey, I am also facing the same problem. Your post is the only one could find, in regards to that topic. I am wondering if you figured it out by now? Also I’ve looked into the 5.1 patch notes but couldn’t find it in there. Very weird.
Ended up discovering a quick solution for my problem.
Simply go to the blueprint and create a variable of type CANVAS PANEL,this way you can SET any canvas panel using that one variable.