BB60c + TG44 – SNA – very strange behavior in 9k-10MHz range

I connect input to output, do store thru calibration and look at a trace. In <10MHz range the trace is unusable at all – it jumps from -30dB to +2dB, on one reading it can be +2db, on second reading it can be -20db…

First picture with min-max hold.
Second picture with 3 traces – min, max and average.

I don’t think it’s a hardware issue, Span mode works correctly in this range.