MyBB redirects to www.www - php

Question

I am working on setting up a MyBB forum with https enabled. I've got TLS set up and enabled and https redirect is enabled by my host.
Direct links like http://www.example.com/index.php and example.com/index.php correctly redirect to https://www.example.com/index.php. But any any attempts to go straight to to https://www.example.com/ go to https://www.www.example.com/. Does anyone have any ideas about what might cause this?
My .htaccess file is as follows (mostly taken from MyBB's default .htaccess setup.)
Options -MultiViews +FollowSymlinks -Indexes
<FilesMatch "\.(php|html)$">
Header set Cache-Control "private, no-cache"
Header set Pragma "no-cache"
</FilesMatch>
#
# If mod_security is enabled, attempt to disable it.
# - Note, this will work on the majority of hosts but on
# MediaTemple, it is known to cause random Internal Server
# errors. For MediaTemple, please remove the block below
#
<IfModule mod_security.c>
# Turn off mod_security filtering.
SecFilterEngine Off
# The below probably isn't needed, but better safe than sorry.
SecFilterScanPOST Off
</IfModule>
#
# MyBB "search engine friendly" URL rewrites
# - Note, for these to work with MyBB please make sure you have
# the setting enabled in the Admin CP and you have this file
# named .htaccess
#
<IfModule mod_rewrite.c>
RewriteEngine on
RedirectMatch ^/$ news.php
RewriteRule ^forum-([0-9]+)\.html$ forumdisplay.php?fid=$1 [L,QSA]
RewriteRule ^forum-([0-9]+)-page-([0-9]+)\.html$ forumdisplay.php?fid=$1&page=$2 [L,QSA]
RewriteRule ^thread-([0-9]+)\.html$ showthread.php?tid=$1 [L,QSA]
RewriteRule ^thread-([0-9]+)-page-([0-9]+)\.html$ showthread.php?tid=$1&page=$2 [L,QSA]
RewriteRule ^thread-([0-9]+)-lastpost\.html$ showthread.php?tid=$1&action=lastpost [L,QSA]
RewriteRule ^thread-([0-9]+)-nextnewest\.html$ showthread.php?tid=$1&action=nextnewest [L,QSA]
RewriteRule ^thread-([0-9]+)-nextoldest\.html$ showthread.php?tid=$1&action=nextoldest [L,QSA]
RewriteRule ^thread-([0-9]+)-newpost\.html$ showthread.php?tid=$1&action=newpost [L,QSA]
RewriteRule ^thread-([0-9]+)-post-([0-9]+)\.html$ showthread.php?tid=$1&pid=$2 [L,QSA]
RewriteRule ^post-([0-9]+)\.html$ showthread.php?pid=$1 [L,QSA]
RewriteRule ^announcement-([0-9]+)\.html$ announcements.php?aid=$1 [L,QSA]
RewriteRule ^user-([0-9]+)\.html$ member.php?action=profile&uid=$1 [L,QSA]
RewriteRule ^calendar-([0-9]+)\.html$ calendar.php?calendar=$1 [L,QSA]
RewriteRule ^calendar-([0-9]+)-year-([0-9]+)-month-([0-9]+)\.html$ calendar.php?calendar=$1&year=$2&month=$3 [L,QSA]
RewriteRule ^calendar-([0-9]+)-year-([0-9]+)-month-([0-9]+)-day-([0-9]+)\.html$ calendar.php?action=dayview&calendar=$1&year=$2&month=$3&day=$4 [L,QSA]
RewriteRule ^calendar-([0-9]+)-week-(n?[0-9]+)\.html$ calendar.php?action=weekview&calendar=$1&week=$2 [L,QSA]
RewriteRule ^event-([0-9]+)\.html$ calendar.php?action=event&eid=$1 [L,QSA]
<IfModule mod_env.c>
SetEnv SEO_SUPPORT 1
</IfModule>
</IfModule>
#
# If Apache is compiled with built in mod_deflade/GZIP support
# then GZIP Javascript, CSS, HTML and XML so they're sent to
# the client faster.
#
<IfModule mod_deflate.c>
AddOutputFilterByType DEFLATE text/css text/html application/xhtml+xml text/xml application/xml text/plain text/x-component application/javascript application/x-javascript application/rss+xml application/atom+xml application/json application/manifest+json application/x-web-app-manifest+json application/vnd.ms-fontobject application/font-sfnt application/font-woff application/font-woff2 image/svg+xml image/x-icon
</IfModule>
# Note: You are able to choose a different name in the Admin CP. If you've done that you need to change it here too
<Files "error.log">
Require all denied
</Files>

Answer 1

This turned out to be a browser caching issue.