I’m not seeing this here using Rhino 6.13 which will soon be the next service release, can you post the 3dm you used in the video please? I believe the issue is https://mcneel.myjetbrains.com/youtrack/issue/RH-43492 which was fixed for 6.13. I can test your file or you can choose ‘service release candidates’ from Options>Updates and Statistics>Update Frequency, then click ‘check now’.
I believe this is https://mcneel.myjetbrains.com/youtrack/issue/RH-45510 which is still an open bug. I found a manual fix listed on the bug report that may help in the meantime…
Use the command UnweldVertex
Drag a fence selection over your mesh to select all the vertices>Enter
Run the Explode command on the mesh
Run Join on the mesh
If that fixes the issue for your mesh, please let me know and I’ll add this thread to the bug report. If you can upload the 3dm you used in a state that shows the issue that would help too. I reproduced it here copying your form and the manual fix worked without destroying the UVs.