Could you please re-start your TS (the dev instance for example)
and try doing the incremental refresh after (a fresh start)?
Re-starting TS would trigger Backgrounder jobs cleaning up Temp space.
This would bring the next refresh task to create a new temp folder,
so you would be able to test if the erratic behaviour is repeated.
If it doesn't help, please, open a case to Tableau Support.
Hi Yuriy, thanks for helping. I tried cleaning the temp directories and restarting my whole server, to bad it didn't help. I will open a case with the support team.
One thing I did find out was, that uploading a dedicated dataconnection (instead of one in my dashboard) the incremental updating works!
Arnoud, thank you for the follow-up.
Though I've got nothing to help with your problem,
I'm curious to see how the case would be resolved.
I finally resolved it by removing the dashboard and datasources from the server, then uploading them again.
That remains a mystery, anyway
i'm glad you've got it working.