Originally posted by Fzanco:

Please confirm if this is the correct series of events.
Explored island put portal down, returned to home base. Went back to island packed up portal and went to a new location. Put portal down and instead of returning to home base you returned to previous island which currently has no portal there. Is this correct? If so then yes that definitely sounds like a wierd descync problem

Thats normal Valheim behaviour since the game was launched. Even in single player. The portal updates every few seconds. You can get unlucky with the timing.