- your Plesk configuration is buggy -> ask your hoster
- the www subdomain has a buggy configuration -> check your Plesk or ask in a Plesk forum
The Plesk client is a "closed world". So if that client doesn't work -> installation problem or a specific Plesk configuration problem.
PS: There is a http status 403 - Forbidden checking /.well-known/acme-challenge. But both - non-www and www.
Looks like you have created these subdirectories manual (without the correct permission) or that your Plesk really doesn't understand something, if the non-www-validation works, the www validation not.