If I only run the base in u-center, I already only rarely get a fix. So as long as that is not stable, the other components are unlikely to perform as expected.
I also tested the base with telemetry radios unplugged, and there have been no improvements or stability gains observable. I have also tested a second set of hardware which I had borrowed to see the impact. For a number of tests, there was also a very clear sky. Same problem: rarely a fix, and if so, only short.
Therefore my thought and request to @philip to first obtain a suitable u-blox gnss configuration file for the base, which regularly acquires a stable fix.