Problem:
With multisite install, a "A different domain per language" WPML setting isn't working.
Solution:
Only have one WordPress install (remove all others), then select this option and follow the guide linked below to set up subdomains for each language.
Problem:
After switching language once, the language switcher always links to homepage.
Solution:
Check if the site is using Flywheel (there will be references to it in wp-config.php of the site). Get in touch with Flywheel support to correctly configure the site URL and home URL settings in order to fix this issue.