YUMI is unreliable

Question

I'm using YUMI by Pendrivelinux to make a multiboot flash drive, but it seems to be unreliable. I have a USB 3.0 64GB flash drive and I can get it to boot, but I've had problems. Seemingly sporadically it just doesn't work. YUMI creates the multiboot without any problems, but once I go to boot it I can get problems. The problems I have experienced are:

1. YUMI menu is no longer bootable.

2. When the menu does come up (which usually requires me to take all Linux distributions off then add them back on), they don't actually boot. It either stays on the menu or goes to the boot command line interface (which can come up by pressing Escape on the choose your operating system menu).

These have come either at random or over the process of adding new distributions to the flash drive. I like the YUMI program, but does anyone have any idea why it's being so unreliable? I can get it to work, but often have to add and remove distributions multiple times, and haven't been able to get it to have more then one OS at a time on the 64GB flash drive. The ISO files I'm using and the version of YUMI are not changing, but the result of running it does change.