I recently purchased the 320+ v4.20 and a few times a day I get spikes on my logger software on my laptop. I have it hooked up via USB and generally get normal background radiation counts, but every once in a while I get counts up to 250 for a short period of time (1 to 2 minutes). I have never actually heard it happen or been able to see it happen, I only see it on my logger pro software. Any ideas? Could this be some kind of grounding issue? Another thing is that the device itself doesn't show that the max is 250, it usually shows about 30 to 35 as the maximum CPM.
My guess is the software then. It has many problems related to the serial connection. You could try one of the python programs. If they show the same error its probably the USB port of something related to that. You could try it on another pc too.
GMC-300E+ V4.20 with sbt-11a alpha tube
My statements are "stuff-a-hobbyist-says" and not in any way professional.
It is a very function issue with 320+ v4.20 which problem it's installing on the laptop so you need to arrange data and then compiled them and also your USB port in a laptop so replace USB and you get it full