What is the value of $page['content'] in custom front page?
$page[content] returns the content for the current page, whatever that may be.  If a view is set at the content, it would return the view, or a node, or a block in the content region or anything else set to show in that region, either through the UI or programmatically. It returns rendered html for all elements in that region.

Chances are under blocks, that view? is no longer listed to render in the main content region as a result of whatever setting changes you made.

If it's a view and set as a block you can modify it under the blocks page, block configuration to show in the region.