I never heard of someone's success in using a Bitcoin core in a USB flash drive.
It shouldn't be a problem, I've seen many people use an external hard drive for their blockchain. It works as long as the USB port can provide enough power and doesn't accidentally gets unplugged.
I've successfully downloaded a pruned Bitcoin Core to
/dev/shm, which has less space than most USB sticks.
your chainstate directory will not be pruned and will continue to grow as the chain syncs
~
(I can't find accurate figures of how big both are at the moment though).
My
chainstate directly is currently 4.8 GB.
Bitcoin Core shouldn't launch with that parameter since it's below the minimum size, are you sure that you're using the correct shortcut?
I checked, and it doesn't just ignore the setting:
Error: Prune configured below the minimum of 550 MiB. Please use a higher number.
On Linux, this works just as expected:
bitcoin-qt -datadir=/tmp/bitcoin -prune=550
I'm not a Windows user, so I can't really tell you what goes wrong. I'm curious though: why use a USB stick instead of just normal storage on your system? Pruning to local storage is going to be a lot faster than a USB stick.
All you need is 6 GB of storage, preferrably on SSD.