Do you have an Add-History method in any activity or any Audit Note in flow shapes? It's a problem with addition of history. Looks like a too big line of history has been added and that is where it is failing.
Looking at the arror it is clear that you are trying to insert 257 CHAR in 255 CHAR size of column. YOu may want to test the feature with smaller values and test again. Or increase the size of the column to test.