Computer shuts down after UPS installed

We recently installed battery backup UPS devices on all machines in our small office. They all seem to be working fine, except one user reports the computer shutting down (and losing any open work or programs) after a period of time. I checked and adjusted power setting as far as sleep, hibernate, shut down etc. We do not use Sleep or Hibernate functions in this office, but I do set monitors to turn off after 10 minutes, HDD's to shut down, etc.

So after I checked those settings, the computer was fine for awhile. Now suddenly as of last week, the computer is shutting down on its own once again. It appears to be a full-on shutdown. To bring it back up, we have to actually press the power button on the tower, the BIOS splash screen comes up, enter domain login and everything. There is no "resume from hibernate" or move mouse to wake up the machine. It's fully shut down, after something like 15 to 30 minutes or so.

I checked power settings again, and the only thing I could see was "Allow Hybrid Sleep" was set to On when the machine is plugged in. Everything else seemed to indicate it would not sleep or hibernate or shut down as long as the machine is plugged in.

Any thoughts as to why this could be happening?

Is the ups controlled by the pc some have a connection to the pc which can force it to shut down if a fault is due. Whate do the event logs say about the shutdown it may tell whats shuting it down

Is it one UPS device for each computer or it's a large UPS for all computers?
Did you check the voltage settings on the UPS (input and output) and also on the computer power supply?
If you have a one UPS device for each computer and the problem is only on one computer, try to switch the UPS with the another computer. If the problem follows the UPS you will now that it's the UPS that has an issue.