+1 seems to fix it for me too
Even when I open the timeline on a different machine or try anything to break it. legendary stuff, i dont even know what to say.
absolutely legendary, i made a tiny version that only does the Action fixing and nothing else , so its easier/faster use if you dont need all the other functionallity, all credits to @john-geehreng however
Better version here:
fix_corrupt_action_only.py (3.6 KB)
and yes i know how stupid of a hack this is , its not clean code as, but it works 
(fixed the issue where i required a custom named sequence, this is just the fix now). this should also iterate over all the sequences you have selected i hope