R&S FSW Signal Analyzer_Level LO2 Issue

[seebeck]

Hi Folks，

I am working on an RFHW team where I need to use a lot of RF instruments.
Our laboratory bought many many RF instruments such as signal generator and signal analyzer from R&S or Keysight.
In recent years, Lab have purchased many R&S FSW series signal & spectrum analyzer and they're used to design/measure RF circuits or RF products. 
Strangely, abnormal rate of "Level LO2" showed a rising with the prolonged period of course, the "Level LO2" is almost like shorthand for "Level of Local Oscillator 2" and the check result was less than the lower warning threshold during "Self-Test" or "Self-Alignment". This problem could have affected the amplitude level's results, including analog domain and digital IQ demodulation.
Please see the plots for details as attached.
We repaired this problem units back to back, have any others of our friends fared hardly?