I was just helping a user with a mod that used to install fine - but now fails with an installer error.
Under the fomod directory, info.xml and ModuleConfig.xml both specified UTF-16 in line 1. This is no longer valid.
Notepad++ with the XML syntax checker also flags it as invalid.
I had him replace UTF-16 with UTF-8 in both files. Vortex now installs it without issue.
This is just a heads-up. This syntax used to be the recommended one.