I ran into this problem as well, I have a groom with around 1 million strands. I followed the epic documentation to apply the root uv using the Maya python script that’s provided in the docs. Maya also “froze” for me while following the steps but I noticed that a single core on my cpu was still under full load so I just left it and eventually it completed successfully. Maya was frozen on my computer for around 48 hours… but it eventually did work. i also noticed that it completely maxed out my ram at several points during this process, I have 32 gb ram. If you can I would recommend splitting your groom into sections of about 300k strands then the whole process will go smoothly without Maya locking up for a ridiculous amount of time but if that’s not possible you can just wait. I just let it go over a weekend when I wasn’t using my computer for work anyways.