I was finally able to reprodice this issue, That's the good news; the bad news is there is no fix that can be done to fix this in Unraid. UD uses some built in functions to perform the script file operations. I can find no solution for Unraid to fix this. This only occurs when Private Browsing in Chrome and appears to be a bug in one of Chrome's security features causing POST failures in specific circumstances. There are no other instances of doing things like UD does in Unraid, so this should not show up anywhere else.
There are several options to deal with this:
Turn off security in Chrome when Private Browsing.
Turn off security for Unraid only when Private Browsing in Chrome.
Don't use Chrome Private Browsing when using Unraid.
This comment was not very helpful at all, and was honestly quite annoying.
There was an issue when some characters (e.g. '<', '>', etc) are used in file names that will cause a php warning and fail a file save or edit. I've added some code to deal with this.