My bluetooth connection AND usb bus cycles on and off after 30 minutes on my mini/high sierra

Hi, hoping to find some help with an unusual problem. Shortly after getting a new SSD (and High Sierra) for my mini (mid 2011) last month, the blazing speed was "checked" after 30-45 minutes of Adobe work. Specifically, external usb drives unmounted at random and bluetooth mouse cycles on and off, followed disconnection idenitified by a flashing zig-zag strikethrough on the bluetooth menu icon.

Out of warranty, obviously. My tech contractor for my apple products has tried several diagnostics and attempted solving the problem by among other things using terminal, disconnecting all usb drives and trying one by one, switching me to another wireless mouse as well as a vintage usb mouse. It keeps exhibiting the same behaviour, though the last time he looked under the hood and fiddled with something, a week ago, it worked for about 2 hours then same old problem.

The new ssd doesn't seem to be running hot and apps (particularly Adobe CC) are working fine.

16GB RAM

Any suggestions?

Thanks