This one is difficult to post a screenshot of considering the placement, which is why I'm posting a wireframe.
I can post a proper screenshot if requested, but it would likely be considered NSFW.
When you adjust the Thigh Tone (pack_leg3_Thigh Tone.ccslider) slider from Ultimate Morphs in either direction, a single vertex on the center line of the body near the beginning of the butt cheeks is moved unintentionally.
When Thigh Tone is negative, it causes a spike. When it is positive, it causes a hole.

Here's the content information for the morph.

Definitely a bug. I suggest opening a ticket in Feedback Tracker so RL can fix it.

Done!
https://www.reallusion.com/FeedBackTracker/Issue/Incorrect-deformation-when-using-Thigh-Tone-from-Ultimate-Morphs

... in the mean time can't you use the "Edit Mesh" to correct those errant points and polys?



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That's what I've started doing. Not sure why I didn't think of it before.

you have to Adjust bones->Body Auto-Position, then adjust floor contacts before you use the morph.