Sometimes unable to copy via USB

[Spike-from-NH]

I have SFM 6.16.0 running on a Samsung Tab A 8 running Android 8. It has a microSD slot but nothing is in it. I attach a thumbdrive to the microUSB 2 port using an OnTheGo adapter. When I tap Internal, SFM gives me the options of both SD and USB. I can examine the thumbdrive's files by selecting either. When I try to export files, SFM instructs me to gain authorization, but then throws a pop-up, "SD card and USB device paths cannot be the same".

Bug consistently appears when adaptor and thumbdrive are installed when SFM starts. Does not appear (and shows only Internal and USB as destination options) when SFM is started first.