This sounds very much like flaky wifi. I don't know how long a camera has to be offline before Nest will alert you to but for us the default is 6 minutes and it may be longer than that for Nest. You can control the Camect delay from the alert settings if you don't want to know about these outages.
When your camera drops off, Camect retries the connection immediately and if that fails it will retry every 6 minutes or so.
If you want to verify that it's wifi, you need to check with the Nest app as soon as possible after the connection drops, or else you have the possibility that the connection dropped, Camect failed to re-establish, the wifi then comes back, and the camera is online by the time you check but before Camect has tried again. (So, I'd set the alert delay to 1 minute and check as soon as you get the alert.)