Ok what you didn’t rule out here is the received signal strength at the Airport Express where you’re seeing a problem.
Moving the suspect Airport express to the other location in the house only confirms the Airport Express itself is ok, not that it gets a usable signal in it’s original location. Neither does moving the good Airport express to the bad location prove anything.
What I asked you to try was to swap the Pi’s over - plug the good Pi into the Bad Pi’s Airport express - at the same location, not bringing the suspect Airport Express to the good location. From the package loss you showed you do have a network connectivity problem, my guess is either power adaptor or the wireless signal to the Airport Express in it’s particular location in your house.
I did swap the power supplies. One is the supply that shipped with the Pi B, the other is a 2A iPad charger.
I have tried three different Ethernet cables.
I haven’t been able to reproduce that packet loss:
30 packets transmitted, 30 packets received, 0% packet loss
round-trip min/avg/max = 59.352/193.615/326.807 ms
The bad Pi is actually line-of-sight with the router. The good Pi has two concrete walls between it and the router. In both cases, the Airport Utility rates the signal strength as “Excellent”. RSSI: -54dBm and -64 dBm
If my router is the issue, then why is only one device having network problems? And, why did I not have problems when running Alpha 4, which was yesterday afternoon?
It’s not odd at all. It’s well known that a B+ requires less power than a B - this was one of the bullet points when the B+ was released.
Also if your B is an old 256MB model they are prone to having the polyfuses fail - they go high resistance which causes excess voltage drop across the fuse, thus you get a low voltage situation even if your power supply is good.
To confirm this you would need to measure the voltage between TP1 and TP2 or try powering it via GPIO. (Guides on the internet)
The power input circuitry of the B+ was completely redesigned compared to the B exactly due to the shortcomings of the power input design of the B.
Apple chargers are also well known to not be suitable for powering Pi’s - none of my Pi’s will run reliably off my iPad charger - which only outputs 4.3 volts with a Pi connected. If you have access to a voltmeter try measuring across TP1-TP2 and you will see. (Anything less than 4.75v is unacceptable)
You really need to be using a power adaptor specifically designed for the Pi as most USB chargers are not suitable.