It appears to be your problem is with .htaccess file, which is confusing the browser. Here's mine, removed some SSL settings only. Can you try to replace your .htaccess with this? After do a CTRL + F5 on your main page. BEFORE doing that, can you also share your .htaccess? line 13 is the problem it seems like...
# Allow access if Flarum is installed in a subdirectory,
# but another .htaccess in a higher directory denies access.
<IfModule mod_authz_core.c>
Require all granted
</IfModule>
<IfModule !mod_authz_core.c>
Order Allow,Deny
Allow from all
</IfModule>
# Fix for https://httpoxy.org vulnerability
Header unset Proxy
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteRule ^vendor/(.*)?$ / [F,L]
RewriteRule ^storage/(.*)?$ / [F,L]
RewriteRule ^config.php$ / [F,L]
RewriteRule ^.git/(.*)?$ / [F,L]
RewriteRule ^api(.*)$ api.php [QSA,L]
RewriteRule ^admin(.*)$ admin.php [QSA,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule !^assets index.php [QSA,L]
# MultiViews can mess up our rewriting scheme
Options -MultiViews
# Autoindex will list all assets files which is not so good
Options -Indexes
</IfModule>
<IfModule mod_deflate.c>
# Compress all output labeled with one of the following MIME-types
<IfModule mod_filter.c>
AddOutputFilterByType DEFLATE application/atom+xml \
application/javascript \
application/json \
application/vnd.ms-fontobject \
application/x-font-ttf \
application/x-web-app-manifest+json \
application/xhtml+xml \
application/xml \
font/opentype \
image/svg+xml \
image/x-icon \
text/css \
text/html \
text/plain \
text/xml
</IfModule>
</IfModule>
# Configure cache expiry for different file types
<IfModule mod_expires.c>
ExpiresActive on
ExpiresDefault "access plus 1 second"
ExpiresByType text/css "access plus 1 year"
ExpiresByType application/json "access plus 0 seconds"
ExpiresByType application/xml "access plus 0 seconds"
ExpiresByType text/xml "access plus 0 seconds"
ExpiresByType image/x-icon "access plus 1 week"
ExpiresByType text/html "access plus 0 seconds"
ExpiresByType application/javascript "access plus 1 year"
ExpiresByType application/x-web-app-manifest+json "access plus 0 seconds"
ExpiresByType text/cache-manifest "access plus 0 seconds"
ExpiresByType image/gif "access plus 1 month"
ExpiresByType image/jpeg "access plus 1 month"
ExpiresByType image/png "access plus 1 month"
ExpiresByType application/atom+xml "access plus 1 hour"
ExpiresByType application/rss+xml "access plus 1 hour"
ExpiresByType application/font-woff2 "access plus 1 month"
ExpiresByType application/font-woff "access plus 1 month"
ExpiresByType application/vnd.ms-fontobject "access plus 1 month"
ExpiresByType application/x-font-ttf "access plus 1 month"
ExpiresByType font/opentype "access plus 1 month"
ExpiresByType image/svg+xml "access plus 1 month"
</IfModule>
