trying to install Linux Mint beside W10 Pro

marc

my board is a UP^2 w 8 GB of ram, 64 GB of drive, pentium quad core, secondary 500 GB ssd external drive via usb. W10 Pro is running on this machine without a glitch for more than 6 months.

After a certain numbrer of tries, I succeed at last to install a Linux flavor (mint, 19.1 "Tessa" 64 bits) on an external SSD (via USB3 link).
/ and home are created, files are copied, Grub2 has even been able to find a place on the local UP board ssd drive (but not on the external one).
The UEFI boot selector see a Windows drive and a Linux drive, and I can switch from windows to Linux... so far, so good
but I have kernel panic as soon as grub has been launched

did someone succeed with such an OS config ? and if yes, what sort of trick should I use ? or is this kind of configuration definitely need an Msata drive ?

cheers
Marc