Info panel says they are groups. Looks like some of my groups appear in this tag list. In the info panel the option to exclude them from tagging is greyed/not available. Still no idea how they ended up in the tags list, nor the reason for such a feature.
I would suggest that perhaps your database is damaged. The info panel indicates that the Bolduc Group you have selected is located inside the Paperless>Mobile Sync Group, even though it appears to be inside the Tags Group. Try running the Verify & Repair command and see if it reports any errors.
In DEVONthink, hold the Option key and select Help > Report Bug. Please send screencaptures but do not blur the data as there may be clues we can glean.
This group was probably replicated and one instance moved to the Tags group, the other one is in still the Mobile Sync group (as replicants inside the Tags group aren’t marked as replicants in the Info panel).
Nothing in the manual as there is no practical use for replicating groups to the Tags group, that I can think of. I would expect that it has to be something that you did in the past, even if inadvertently.
Also, the Mobile Sync Group itself is a relic of the DEVONthink to Go version 1 days and is no different now than any other normal group in the database.
According to the video you sent into Support, the group was dropped onto a Tag, effectively tagging the group itself. A Tag replicant was created in the Tag group, as is the normal operation. The group had to have been moved out of the Tag group it was in, leaving the replicant in the Tags group as anormal group, showing the location of the original.