PothosSDR-2021.05.01 - Tx Calibration: MCU error 5

Hello

My board is LimeSDR-USB rev 1.4
I’ve installed PothosSDR-2021.05.01 and updated FW and GW to the latest versions.
As you know, GNURadio performs automatic calibration before start.
So, channel A calibration is ok, but channel B always fails.

I’ve tested calibration via LimeSuite, channel A calibration is ok, but channel B always prints message “ERROR: Tx Calibration: MCU error 5 (Loopback signal weak: not connected/insufficient gain?)”. But with enabled MIMO calibration is performed successfully.
I did read old topics and the wiki, nothing could help me.

Is it a hardware bug?
How can I fix it?