Thats because Sub-Subdomains arn’t covered. please read:
all the details are in that post
a .htaccess rule like below can automatically redirect to without the www.
RewriteEngine On
# Force HTTPS
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
# Remove www.
RewriteCond %{HTTP_HOST} ^www\.(.*)$ [NC]
RewriteRule ^(.*)$ https://%1/$1 [R=301,L]
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