From my testing so far, it seems that either using the cellular assisted gps mode or cgps is what is causing the serial port issues. If I turn off the cellular radio and dont go through any of the config, it is able eventually able to get a fix unassisted and doesn't have any issues with the serial port. gpsmon works fine and I can go back and forth between that and ttyGSM3 without issue. After maybe 20 minutes of running I went into cgps, it didn't seem to get any gps data (no text lines refreshing below the gui), and then at that point the serial connection broke and I had the same issue as before: no data into cgps or gpsmon, cant type in ttyGSM2, and ttyGSM1, etc.
Using assisted mode and manually going through the cellular setup commands until I am able to successfully ping google.com before turning on the gps, I am amble to get a fix within a minute or two as expected. Entering gpsmon only, then exiting it and trying to access ttyGSM3 gives the device or resource busy error. If I keep trying to access it, ttyGSM3 will eventually open, but won't show any data, and reentering gpsmon after this point will make it fail to recognize the gps and nothing will work until a restart of the raspberry pi + gps/ a cold boot. (pic attached)
I dont think its an issue with the raspberry pi itself, since it remains responsive even when minicom/ the serial connection stuff starts breaking. It doesn't seem to be overheating or anything like that, its cold enough outside where I am that it stays barely warm to the touch when its outside. Conversely when its inside and warms up more I still have the same issues.
Another thing I am seeing is when I have some of those cellular commands for PDP and IPV4 fail it shows up in the hologram dashboard as a "session without data". Im thinking that may be the cause of the issues with the cellular commands, but in terms of how/if that could affect the serial connection I have no idea.
