If synology uses RTMP or something like that check the Network Port Settings and enable all protocols to see whether that helps.

I once had similar problems with a different type of camera. In my case it helped to reset the camera password to blank and retry. You might want to try that.

My RLC-410W all connect to 5GHz when they have the choice between 2,4 and 5G. So it may be something related to the battery powered cameras in order to save energy. It would be great though if this were user configurable ...

@user_594250775031824_594250775031824 Check the network port settings on the camera.