this occured to me few days ago when for the first time i tried to use OpenMultiBoot for the purpose to have more room for plugins and other stuff in my VU solo2
instead to use Universe as i did for the past ......so now I want let everyone how I solved.
in my case I'm using a kingstone 32gb usb pen
first of all very important is to format the usb pen with the utility of Windows 10(in my case) choosing from menu "exFAT," and allocation dimension:set
default(predefinito),option quick format
in this way I solved
my opinion:the issue is that formatting in fat32 some files written in the usb pen cannot be completily deleted by the format utility(in EXT4) of BlackHole
or another issue could be that this occures with very large memory capacity of usb pen (like mine of 32Gb)
try and let me know
sharing knowledge is the purpose of forum users
let me know asap