Suddenly Chromebook won't boot into Linux from USB, possible noexec problem?

After over two years of successfuly having a dual-booting Chromebook, mostly using the Linux side of things, I booted into ChromeOS to run something particular and when I tried to boot back into Linux it will only get as far as

SeaBIOS (version rel-1.11.0-54-g248459e-MrChromebox-2018.09.12)

Press ESC for boot menu.

Booting from USB Device...

and then it just stays that way. I’ve waited up to an hour, and it just stays on that screen. Unless I press shift to get into grub and then replace Booting from ‘USB Device…’ with ‘GRUB’. But that’s it. It wont boot into the GRUB menu either. I know the USB drive is readable and still has all the appropriate files, all the files in general, as I can see it when I boot into ChromeOS.

I’ve been trying to solve this my self, but I haven’t got much to go on other then when I retried Mr-Chromebox’s firmware-util.sh to see if reinstalling/updating the RW_LEGACY Firmware might help (it did not) this error was printed:

firmware-util.sh: warning: firmware-util.sh: warning: script from noexec mount; see https://chromium.googlesource.com/chromiumos/docs/+/master/security/noexec_shell_scripts.md

Is there a way to change my noexec seetings? Is that what’s keeping me from booting? It maybe can’t read the script on it?

Any help would be so appreciated!