Lime Test Mini Loop test failed

I have two Minis meanwhile.
Loop test failed with identical protocol results. I did this on two different PCs.

[ RF Loopback Test ]
->Configure LMS
->Run Tests (TX_2 -> LNA_W):
CH0 (SXR=1000.0MHz, SXT=1005.0MHz): Result:(-13.8 dBFS, 5.00 MHz) - PASSED
->Run Tests (TX_1 -> LNA_H):
Failed to read samples: No samples received
CH0 (SXR=2100.0MHz, SXT=2105.0MHz): Result:(-14.0 dBFS, 5.00 MHz) - FAILED
->RF Loopback Test FAILED
=> Board tests FAILED <=

It seems to me, this is not an individual failure but systematic.
With LimeSuite I could upgrade the gateware to 1.28 on both boards.
SDR Console works, some crashes give no output. A restart helps
Rx and Tx antenna automatic.
Don’t know what to do?
My hope was, the replacement will help. I know tho guys in the neigbourhood with
proper test results. The bords were delivered by the same office.
The dealer offered me a replacement, this was generous but didn’t fix the