Along with the suggestions above (good one from Grimaldi) regarding the country code - it's important that the USB environment remain as static as possible. un/plugging devices over and over provides a non-deterministic experience. There is a serial port mapper utility that comes with StellarMate that may be worth the $50 to you - there are also scripts that this community has produced that require commandline execution by the user.
This process of mapping devices one at a time as they are connected to your rpi3/4 really made a big stability improvement in my rig (network included). HTH