Mac mini 2018 problem with USB pen drive
This is most likely Bluetooth interference from radio frequencies.

Your choice is probably to not use a USB or get another device.


  This means that any USB 3 port, cable or USB 3 device can emit radio frequencies that may cause interference with any Bluetooth devices you using in your computer.


(Source)

Another quotation:


  The issue is that USB 3.0 hard drives can emit radio frequencies that interfere with Wi-Fi and Bluetooth transmissions on the 2.4 GHz band, especially when placed near the antennas in your laptop.


(Source)