Hi,
I know this thread is a few days old, but I also encountered a problem with pressure sensitivity from my Wacom Intuos (CTL-480) in Affinity Designer, and it's not listed under 'known issues' on the update page, but I didn't want to make a new thread to report it.
The brush settings were set for pressure to control size & flow, but it was not detecting changes in pressure. However when I went to the Wacom Tablet Properties which come with the drivers, and added Designer as an application, it began to work without any further changes.
When I deleted it, it stopped detecting pressure once again.
I've not been experiencing any such problems with any other programs which I use my tablet with (Photoshop, Illustrator, Drawplus, SAI), so I don't think it's to do with tablet drivers, however, I updated the drivers just to make sure, and the problem persists.
Until it is fixed though, 8q8, this might fix the issues for you. xP