1. I get AC bug from Evard's in the Lowerdark - Howling Canyons
2. I relog to fix it but my location is reset to OOC starting area + spawnpoint (Garden of the Lost)
3. The DM ports me back to the rest of the party, things go as normal
4. I encounter the stuck inventory item bug (cannot equip helmet) while we are walking in the Moldmire, I relog to fix it
5. I log back in in the area where the DM had ported me, in Lowerdark - Howling Canyons
Never encountered this bug before.
Did you at any point change your gamespy ID? (Or whatever it is called now)
Since the vault is no longer tied to them, changing them seems to reset your starting point. In this case, likely why you went to the Garden of the lost.