Symmetrize worked yesterday, but not today

[MrJRules]

I recorded a video tutorial for my students where I demonstrated Symmetrize in the UV editor using Mio3 tools. Worked like a charm. Now, a student contacted me and said the symmetrize option was not working. I am on a discord call with him now and we are both having the same exact problems. We have the Susan model, mess with the face uv's on one side, symmetrize, and the UV's break.

Before:

After, broken:

Working, yesterday...

Here is the video at the time where I use the feature... yesterday. https://youtu.be/BiuZRgokPe8?t=1586

I now have 50 students who are getting stumped at this. Nothing on my computer has changed, I have not updated blender, I have not done anything else but use blender for the past few days... not sure how a function that worked yesterday all of a sudden does not work anymore... not only that, but it errors out the same exact way for both myself and the student helping me to debug the issue. Any help would be greatly appreciated.

4.3 is being used.

[mio3io]

I tested it, and there seems to be no problem with its operation.

Possible causes are that the threshold is set too high, or that the 3D side is not symmetrical.
The higher the threshold, the less accurate the results will be.

This symmetry function assumes that the topology on the 3D side is strictly symmetrical, so it is desirable to set the threshold as low as possible.

It may also be interfering with other add-ons or settings.