Faderport 8 - Firmware update 2.02 to 3.21 - UC v3.1. fails

I'm having some problems at the moment with my Faderports (Classic & FP8).
Universal Control v3.1.0.53214 for Windows, OS is Windows 10, Studio One 4.5.2.

Presonus tells me 'A firmware update is currently required for full functionality'

UC tells me to Upgrade 2.02 to Version 3.21 on my Faderport 8.
Nothing besides UC is runiing on the freshly bootet PC.
When I start the Update, UC works around 4 minutes 'updating' and then tells me the update was successful.

While the update is running FP8 shows 'Please Wait 0%' and stays at 0% the whole time.
When UC tells me it's finished, FP8 tells me 'Update failed - Please Power cycle'.

Does anyone have in idea how to fix that problem?

Walter