I installed Ubuntu 19.04 to a 128GB flash drive with the intent of booting my Acer 14 Chromebook from that so I can use it as a development environment for school. Install seemed successful and I was able to boot from that flash drive on my first attempt, but since then my Chromebook has stopped recognizing the drive-- it simply doesn't list it when I bring up the SeaBIOS boot menu. I've tried this on two other (PC) laptops and gotten similar "no bootable device" messages when attempting to boot.
I've loaded up my Ubuntu live stick and in the disk utility I can see the 128 GB volume. It says "Master Boot Record" after Partitioning and "Linux (Bootable)" after Partition Type. I don't understand why this isn't booting, or how I can diagnose or repair it.
Flash drive is Sandisk Cruzer Snap, if that's relevant.