When you want to use SSL with htaccess on xserver

Access restrictions and redirect settings are set for the setting domain
Temporarily disable them until the update is completed.

Link: https://www.xserver.ne.jp/manual/man_server_ssl.php

It's troublesome to have to disable .htaccess every time you set up and update SSL. It's a workaround.

There is such access when setting SSL.

access.log

hoge.jp **.**.**.** - - [06/May/2022:10:19:17 +0900] "GET /.well-known/acme-challenge/Hoge123Fuga456hoge789Fuga HTTP/1.1" 200 87 "-" "Mozilla/5.0 (compatible; Let's Encrypt validation server; +https://www.letsencrypt.org)" 

Therefore, you should exclude this access. example:

.htaccess

<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{HTTP_USER_AGENT} !letsencrypt #これを追加
    RewriteRule ^(.*)$ public/$1 [QSA,L]
</IfModule>