SmartMerge/UnityYAMLMerge returns "bad allocation" error

This isn't a promising start. The first time I've tried the SmartMerge (using it as an external tool in PlasticSCM using the instructions here, but the same thing happens if I do it from the command line) it bombs out before doing anything else with a "bad allocation" error.



I suspect this is because the base scene file is from Unity 2019.3.15f1 and the source and dest files are from 2019.4.9f1. Are we just out of luck? The only way I can think to solve this is to try to check out the base files and then upgrade them to 2019.4.9f1, then use THAT as the base. It seems very kludgy and prone to disaster, though.

 

Update: I grabbed the original files that the branch was created from and updated them from 2019.3.15f1 to 2019.4.9f1. I then tried to use those files to merge, with the command
UnityYAMLMerge merge -p (basescene) (sourcescene) (destscene) (output)

I still get the bad allocation.

If anyone from unity wants me to send the scene files to them, just let me know. Don't want to post them here as they're a bit confidential.