Global VPN Client connection through Galaxy S21 Hotspot

This is pretty specific, but I have confirmed complaints from a user that they cannot connect to the office VPN through their new S21 phone as a hotspot. Their older Samsung phone and other cellular hotspots - no problem. Just with their new S21 phone.

Office router VPN is a Sonicwall TZ500, GPVN client on Windows 10.

Here's the log message:

I researched the error, and tried all of the solutions online I could find, but still no success.

Updated client to enable the "restrict first ISAKMP packet" option.
Checked the router's settings, made sure MTU was 1400 and unchecked the "Fragment non-VPN" option.

I also found online forums where a couple of people reported the same specific thing with no resolution.
Anybody have any ideas?