Apache reverse proxy – URL without / is refused

I use reverse proxy to show backend server content for a subdomain.
The subdomain.mydomain.com (server A) should display content of server with IP 123.123.123.123 port 1111 (server B).

Virtual host of subdomain.mydomain.com (server A):

<IfModule mod_ssl.c>
<VirtualHost *:443>
ServerName subdomain.mydomain.com

SSLEngine on
SecAuditEngine On
RewriteEngine On
SSLProxyEngine on
ProxyPreserveHost On
LogLevel warn

<Directory />
    Options -Indexes +FollowSymLinks
    AllowOverride None
    Require all granted
</Directory>

<Location />
    ProxyPass https://123.123.123.123:1111
    ProxyPassReverse https://123.123.123.123:1111
</Location>

ErrorLog /var/log/apache2/error.log

SSLProtocol             all -SSLv2 -SSLv3
SSLHonorCipherOrder     on
SSLVerifyClient none
SSLVerifyDepth 1

SSLCertificateFile /etc/apache2/cert.site/chain_wildcard_site_combined.crt
SSLCertificateKeyFile /etc/apache2/cert.site/key_wildcard_site.key
 
SetEnvIf User-Agent ".*MSIE.*" 
         nokeepalive ssl-unclean-shutdown 
         downgrade-1.0 force-response-1.0

</VirtualHost>                                  
</IfModule>

Virtual host of 123.123.123.123:1111 (server B):

<IfModule mod_ssl.c>
    <VirtualHost 123.123.123.123:1111>
        DocumentRoot /srv/www/site/htdocs

SSLEngine on
RewriteEngine On
SSLProxyEngine on
ProxyPreserveHost On
LogLevel warn

<Location "/">
   Require ip 222.222.222.222
</Location>

<Directory />
    Options FollowSymLinks
    AllowOverride None
</Directory>

<Directory /srv/www/site/htdocs>
    Options -Indexes +FollowSymLinks +MultiViews
    DirectoryIndex index.php
    AllowOverride None
    Require all granted
</Directory>

ErrorLog /srv/www/site/log/error.log
CustomLog /srv/www/site/log/access.log combined
CustomLog /srv/www/site/log/ssl_request_log 
            "%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x "%r" %b"

SSLProtocol             all -SSLv2 -SSLv3
SSLHonorCipherOrder     on
SSLVerifyClient none
SSLVerifyDepth 1

SSLCertificateFile /etc/apache2/cert.site/chain_wildcard_site_combined.crt
SSLCertificateKeyFile /etc/apache2/cert.site/key_wildcard_site.key

        <Directory /usr/lib/cgi-bin>
                SSLOptions +StdEnvVars
        </Directory>

    </VirtualHost>
</IfModule>

If I load URL:

https://subdomain.mydomain.com/dir/

it loads successfully.

If I load URL (without trailing slash):

https://subdomain.mydomain.com/dir

it results error page: ERR_CONNECTION_REFUSED.

Any idea why it is resulting error, when trailing slash is missing?