What I did

I re-connected Q-mass to the flange and tightened the bolts in order to improve the vacuum level.
This improved the vacuum level as before.
Then I tried to measure the residual gas by Q-mass.
Q-mass, hoever, showed a fatal error as shown in fig. 2 --- filament 2 defect.
Actually I could not measure the residual gas as shown in fig. 1 though I could do it yesterday...
It's like "yak shaving".

Next Step

I will open the chamber and install two temperature sensors with indium sheet.
In addition, I will adjust the optics and then close the chamber and do some measurements.