synology ds423+ UPS problem

The NAS is powered by a CPS UT850EG UPS. They are connected via USB cable.

It is set to safely shut down the NAS if the power goes out and does not come back on for 5 minutes.

However, if there is a power outage e.g. for half a minute and then the power comes back on, after a while I notice that both the UPS and the NAS are off, completely shut down.

Logs:

1. the UPS connected to the NAS device has entered battery mode. Estimated battery usage time: 90 minutes

2. The NAS device has not shut down properly.

https://preview.redd.it/eixodwlm9sid1.png?width=1884&format=png&auto=webp&s=d2c257b9fe3a120f5d2670af03d70287e834fb6c

What is the reason? It is as if after the power comes back on it does not detect