It is a bit off-topic and wired, but I know, many of you have a strong IT background and might could help.
If I connect my Raspberry with Openhabian to an USP (APC), it does not run smoothly (i.e. the CUL for homegear is no longer detected, which is connected via USB).
If revert back to normal power from a socket w/o UPS, I don’t have any issues.
I have also a CC2531 (zigbee) and SSD connected at the USB ports.
I know from issues with power supplier not delivering enough power, but this power supply works fine since month.
You do not specify which kind of APC UPS you are using. I have a raspberry pi v3 with a DAC hat with the original power supply connected to an APC BE550G UPS and I do not experience any trouble. When I used a different power supply (an USB charger rated 2A of an old phone) I was experiencing from time to time weird problems.
You maybe interested in monitoring if there are some undervolt events occurring
by using the vcgencmd command.