Hello @joostvandevijver,
thank you for your answer.
I checked the products and I must update them to resync them with Zettle. I did a bulk edit with a dummy edit to trigger post update. Now they synced correctly.
What I assumed was that when the products got updated they will be resynced with correct prices and taxes.
But there must have been any problem with sync maybe from cron or an other trigger.
It doesn’t matter which tax setting is used, like you found out correctly.
but the products must have a post update hook to cause resync and then they are fine in product library at Zettle.
The ticket can be closed now, until I get a vaild reason for the unsynced tax settings.
What ever causes products to get wrong tax setting, could be an other plugin that in incompatible with zettle sync.