Mike if it has an eccentric bottom bracket for tension, these can be cheap OEM items lacking lubricant that can cause squeaks and tension issues. Definitely shouldn't be changing tension with wheel changes, suggests the tensioning device is moving, or your frame is
The hub not behaving as normal for all riding conditions and styles is not normal operation I've experienced as a multi-geared hub lover. Cable tension alignment in the shift indicators is important, and if it's not operating like new, then there's a problem.
There's a Focus Planet TR2 for sale on ebay locally, with a warranty replacement Alfine hub. I enquired and the owner said the shop couldn't solve the shift gremlins and it was replaced under warranty, resolving it.