I've noticed that Red QPD trans-impedance amplifier box has the tendency to switch off REALLY easily, and once it is switched off, I needed to wait for 30 seconds or something before I can switch it on again. It looked as if the board was near the capacity of the breaker circuit or something.

Also two of the four segments of the second red QPD had large offsets.

These were before swapping the amplifier box with the green one.

Once we've swapped the amplifier box, the problem persisted. The box connected to the red QPD was really easy to switch off, was reluctant to come back, and the same problematic channels had large offsets though the exact offset number changed.

When we disconnected the input cable connecting the QPD feedthrough on the chamber and the QPD box, the power switch felt normal and it was possible to switch on and off repeatedly without waiting for a long time.

Probably the QPD trans impedance amplifier is drawing too much current. We're suspicious of something like a cabling problem  of the red QPDs that causes high frequency oscillation, and maybe this is happening for two channels.