Yep, I am. According to their support forums, it looks like it's a fairly widespread issue.
https://forum.g-portal.com/thread/33856-mistlands-update-issues/?postID=128656#post128656

I have a dedicated Valheim server using G-Portal and I backed up the save, changed it over to normal game mode, then changed my steam to normal and started up game and joined server. My character started at the boss stones (starting spawn location) and the world seed was the same but fresh, unexplored and unsullied. I switched the server back to test as well as my steam client and restored the backup again and all the progress made was retained.
How can I do this for my dedicated server but on normal and is it even worth it if essentially all the files are identical to the normal mode?

im having the same issue as Grimm Turd here, anyone has a fix?

i test it on g-portal works fine

Unknown User — Today at 1:06 PM

Gportal Issue:
1) Turn off your server.
2) Ensure that the Valheim+ is enabled under your Gportal settings to make server side mods run.
3) Turn on your server, let it run for a minute, then turn it back off.
4) Connect to your server with Filezilla. Use Filezilla to delete the Valheim Plus files under Bepinex/config and Bepinex/plugins. Leave Valheim+ checked under GPortal basic settings!
5) Turn your server back on and connect.

From a discord discussion. Hope it helps.