1. 【Circuit diagram for CD74HCT4051】
+4.5V
-4.5V
-4.5V
Input
( to OP amp)
COM output
( to OP amp)
CD74HCT4051 is used as a portion of PGA( change feedback resister).
So, this line is connected to high-impedance.

2. 【Capture of Power On for CD74HCT4051】
For just a moment, VEE goes +1.0V then goes - 4.5V
Enable go high before VEE goes -4.5V
(Green）
Vcc 4.5V(Blue)
VEE -4.5V（Orange）

3. 【Problem: COM output　capture 】
Bad part
(Blue)
: oscillation is seen
Good part
(Orange)
Problem:
Oscillation is seen depend on good/bad PCB.
good/bad part is same design but different PCB.
Occurrence is a few times / on 10~100 power on.

4. Question
Do you have criteria ( timing ) about relationship
between S0~S2 , /Enable and Vcc, VEE for Power Up( and Down )?
We can not find the criteria those in data sheet.
2 In customer’s set, Enable ( and S0~S2) start up before VEE goes t- -4.5V.
Do you think this is problem?
3 In customer’s set, VEE goes +1V at a moment.( cause unknown)