Unfortunately, no. I thought it occurred because I didn't assign to each class separately (our LMS is Canvas), but I still had students say that they get error messages.
The only thing that seems to work is when they get the error message, open a new tab, go back to cK-12 and it then allows them to turn it in. It seems to be working for the most part. But it would be nice to be able to use it normally and not have to do the extra step.
Good luck and let me know if it works for you!