It's possible, I suppose, but more likely it's just that some of the components got switched between the various builds. Although some components stay the same across most/all Pis of the same generation (e.g. CPU) the rest of the components (connectors, voltage regulators, etc.) can change based on what manufacturer's components are available/cheapest/etc. The quality of these components can vary wildly, resulting in some Pis seeming to work with a marginal power supply and others not.
I don't have any experience with TeamViewer, unfortunately, to be able to tell you how resource-intensive it might be. What I
can tell you is that Fermentrack shouldn't be actively using all that much processing power, so you should be fine.
Poor WiFi signal strength
absolutely could cause the issues you are experiencing. Every time your controller loses connection to WiFi you're looking at a minimum of ~60 seconds of Fermentrack reporting an error. The antenna on the ESPs isn't the best, so if your Pi is showing marginal connection, your controllers are likely barely connecting at all.
Without knowing the topology of your specific network it's impossible to say whether or not you need to reset the controller's settings, so I would get the additional network hardware in place and just see if the controllers automatically connect to it. If they don't, there is a "Reset WiFi settings" option on the manage device page within Fermentrack. If you can't use/don't want to mess with that, then yes - reflashing the controller is also an option. I recommend flashing the wiring test firmware first (that firmware explicitly resets your controller's WiFi settings) before flashing the BrewPi firmware again.
I thought I added an indicator of signal strength to the "Manage Device" page for Tilts in Fermentrack (the "RSSI" indicator), though I won't make recommendations for how it should be used. If you can get your controllers to consistently connect you could always try a
TiltBridge.
