Plesk Installer reports the following warning:
WARNING: Found one or more domains with mixed-case names. Such domains may have trouble working with the "FPM application server by Apache" handler.
29 Example.com Example.com
#PPP-31339. "Domains with upper case letters may lead to a Plesk bug with ID PPP-31339"
- Plesk Obsidian 26 April 2018.
If update is not possible for some reason you may try the following:
In Domains > Example.com > Hosting Settings rename Example.com to Example.com.old and then do it once again to example.com
Note: In some cases, after changing all uppercase letters to lowercase letters in domain names, the warning about mixed case names may still showing. In this case, the warning can be ignored.