Morrigan

If you have pages you could try adding a custom block with an empty div in it.

Use the support tool. Your cache needs to be rebuilt.

This doesn't sound accurate as the posts from one of my clubs adds nearly half of my forums posts.

.ipsReact_button { filter: grayscale(0%) brightness(100%); } It will make it look normal. The problem is that the default is meant for the heart and doesn't work well on the yellow emojis.

.ipsType_richText img { border: 5px solid #000; }  

Rebuild your search index.

Bugs should always be reported via ticket in the Client Area:
https://www.invisioncommunity.com/clientarea/

There is no way to do this like there was in the 3.0 days. You should likely either post a suggestion or reach out to IPS and explain the issue you're having.
That I know of, the task doesn't need to run in order for it to unlock if they attempt to log in again after their 15 minute timer is up. The task is to clean them up if they didn't attempt again. I THINK!
I know I've never personally had an issue with logging in after I wait through my time out.

There is no way to do that. Only admins and global mods will be able to edit it.

Your theme is a mess and the person that made these edits made them in the WRONG places.
I would personally recommend you create a new theme (fresh no changes). Use the edit theme to change the base colors and then ask how to change the other things after that.
The person that did this theme originally edited framework.css which is a BIG no, no and will cause you nothing but grief as you upgrade.
The theme itself wouldn't be hard to replicate and get working to what it looks like now. It seems to be primarily default with a ton of color edits and some added images.
 
That's my true recommendation. However if you just want to fix it issue by issue and not resolve your core issue this is how you fix your current one:
.ipsBreadcrumb, .ipsList_inline, .ipsList_reset, .cSignedIn, #elUserNav, .ipsList_inline, .ipsList_reset, .cSignedIn { background: transparent; background-color: transparent; background-image: none; }  

This is actually working as intended. The issue you're having there with the big checks showing is that it looks like the image is tiny and the CSS was likely changed. 
.ipsCoverPhoto_container { background: black !important; } Add that to the bottom of your custom CSS to override the behavior.

Find this template:
forums > front > index > forumRow
Find this:
{{if !$forum->redirect_on}} {{if \IPS\forums\Topic::containerUnread( $forum ) AND \IPS\Member::loggedIn()->member_id}}<a href="{{if $isSubForum}}{$forum->url()->setQueryString( array( 'do' => 'markRead', 'return' => $forum->parent_id ) )->csrf()}{{else}}{$forum->url()->setQueryString( 'do', 'markRead' )->csrf()}{{endif}}" data-action='markAsRead' title='{lang="mark_forum_read"}' data-ipsTooltip>{{endif}} {{endif}} Remove it and then find this:
{{if !$forum->redirect_on and \IPS\forums\Topic::containerUnread( $forum ) AND \IPS\Member::loggedIn()->member_id}} </a> {{endif}} And remove it as well.

Themes > Click edit on your theme > front end colors tab > Body background
If this doesn’t change it then you need to talk to the theme author.

If you have Pages you can create a custom block.

CTRL+F in the admin panel for "support" is normally the easiest way but:
DOMAIN/admin/?app=core&module=support&controller=support
Is the normal URL.
Then "something isn't working correctly" and continue. It will clear the site cache which SHOULD fix the missing files issue.

Hamburger Menu > Click envelope > Click "Go to inbox
If you don't have the hamburger menu then you need to fix your custom theme.

In forums > front > index > forumRow Find and remove this:
{{if $forum->hasChildren()}} <ul class="ipsDataItem_subList ipsList_inline"> {{foreach $forum->children() as $subforum}} <li class="{{if \IPS\forums\Topic::containerUnread( $subforum )}}ipsDataItem_unread{{endif}}"> <a href="{$subforum->url()}">{{if \IPS\forums\Topic::containerUnread( $subforum )}}<span class='ipsItemStatus ipsItemStatus_tiny {{if !\IPS\forums\Topic::containerUnread( $subforum ) && !$subforum->redirect_on}}ipsItemStatus_read{{endif}}'><i class="fa fa-circle"></i></span>&nbsp;{{endif}}{$subforum->_title}</a> </li> {{endforeach}} </ul> {{endif}}  

Well the text is likely translatable in the Language.
As far as the look of the labels:
[data-pagecontroller="register"] .ipsFieldRow_label { Change the look here. }