fbai You have written the following:
“As said I use it with Google Wifi and as I recall this requires the UPC modem to be in bridge mode, correct? Are there other settings that would be benficial for this set up? Set up is as follows: UPC Modem -> Googe Wifi router -> switch -> 3 AP wired”
If you set the modem to bridge mode, then you can connect your Google WIFI devices and use them as access points. The WIFI of the UPC modem is then disabled.
If you leave it in router mode, then I would disable the WIFI of the UPC modem before activating your AP’s. Otherwise all these WIFI signals will interfere with each other.
If you do speed tests afterwards and have interruptions only in the WIFI, I would check the configuration of your Google WIFI devices. For this, the community can help better, since I do not use Google devices.