DIAGNOSIS That solid amber light means it's in its factory reset or setup mode, not connected to your Wi-Fi. It either lost its connection completely, or someone held the sync button too long.
FIX You gotta re-sync it like it's new. In the Arlo Secure app, go to Add New Device, select your camera model, and follow the prompts. It'll have you scan the QR code on the camera itself or inside the battery compartment. Make sure you're holding your phone close to the camera when it asks. After the sync, it should blink blue and then go solid blue when it's online.
IF THAT DIDN'T WORK The sync process can be picky about distance. If it fails, move your router and phone much closer to the camera (like in the same room) and try the sync again. Also, double-check you're connecting it to a 2.4 GHz Wi-Fi network, as these cameras don't work on 5 GHz bands.
HEADS UP After a re-sync, you'll likely need to redo any activity zones or specific settings you had for that camera, as those are stored in the cloud profile for that specific device instance.