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.  

indilib.org/forum/general/4787-how-do-i-...assistant.html#36430

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

Read More...