I'm getting really frustrated with this, I hope someone can offer some guidance.
I have 2 raspberry Pis - one in my living room and one in my garage. Over the last 2 weeks or so they have both started becoming unresponsive after some time (time varies). I have tried re-imaging them and replacing sd cards.
They are both raspberry pi 3 and are both on wifi. They are both headless.
Sometimes when I power them up they never become available for connection on ssh. Sometimes they are available for a short time or a few hours then I can no longer ssh to them.
Today I brought one of them up to the study where I have a monitor that I can plug in. Of course it booted fine and all was perfect. I moved it down to the living room and plugged it and and I could never connect to it. I tried moving it around a bit thinking that the wifi signal could be the issue (it's in a tv cabinet) despite my phone reporting a very string signal. This seemed to help and I got it connected (I now think that the wifi signal was a red herring).
After I successfully connected to it I sat with a terminal open all day pinging both pi and they both stayed alive all day.
I went out to the Gym for an hour and come home and they are now both unresponsive again. I tried rebooting them in the same place that they have been responding to pings all day and I am still not able to connect to them.
When they are not responding to SSH I can't see them on the attached devices list on my router.
Does anyone have any suggestions about how to start investigating this?