DIY tx modules tx power factor 100x too low

[dgrat]

I build a DIY slim and a super slim. The tx power on both modules is 77uW if 10mW is set.
There is an increase in tx power if changing it in the firmware to a higher value (but also factor 100 too low).
I checked for an issue in the ufl connector by checking with and without antenna cable connected.
There seems no issue with the tx output because the measured tx power is close to zero if the cable is detached.

The radios bind and link quality seems not too bad (like in JB's yt vids (-40-60 dbm) 1m away @ "10mW").
On the other hand the tx power is clearly less and the modules become relatively warm.

Build

10mW

Unplugged Cable