I have a Raspberry Pi 3 which runs with no problems at home, and 2 identical Raspberry Pi B+ at my office.
One of the B+ units was non-responsive, so I did some testing (note, I do not have a monitor, everything is over SSH).
1. The unit would be ping-able after the usual duration, and as long as it was responding, SSH in would work.
2. After some indeterminate period of time (normally 20-30 seconds), the unit would stop responding to pings and SSH would stop working. Existing connections would time out.
3. ONCE, leaving it alone for about 5 minutes resulted in it responding to pings again, and an existing not-yet-timed-out SSH connection continuing as if nothing had happened. I cannot replicate this.
Moving the same SD card over to my other Pi B+ results in none of the above problems, leading me to suspect hardware issues. I also use the same power supply and LAN cable to eliminate those suspects.
Please advise whether my conclusion is reasonable and if so what I can do.