I finally had some time today to look into removing some of these unknown frames I found in my library. I tried the method from this earlier post and had no success at first using the cut/paste method.
Even when I confirmed I was using the "Cut Tags" tool and not "Copy" the tags were not being removed. I found that this was of course related to my settings for removing ID3v2 not being checked, as typically I don't want this to happen when using the Remove Tags tool. I didn't realize it also affected the Cut Tags tool.
Once I added the check for this option under Remove (all three), the cut/paste option worked and I can confirm the %_id3v2_unknown_frames% were then removed from the selected files as desired. This was an oversight on my part, but hopefully noting it here helps anyone else that is having this issue.