WordPress stripping out tags and replacing with quotes "

Here’s a weird problem that I haven’t had until only recently. (I’ve been using WordPress since 2010 and developing small plugins and themes since 2013.)

On this site (coded by me) and this site (not coded by me), the formatting looks a bit silly – it didn’t when I was developing it originally. I’m also getting the SAME formatting problems on a site that I’m currently developing in the localhost environment.

It seems that WordPress is stripping OUT all my <p> tags and replacing them with quotation marks (“). I Googled this problem and found MANY possibilities.

• It might be a filter hook being applied to the_content() that strips out <p> and replaces it with " so possibly a plugin – but I have only the Developer plugins running on my localhost site, so it’s not that
• It might have something to do with the wpautop() function in formatting.php – I won’t pretend to have read it all nor understand it all, but I don’t really want to mess with the WP Core code…
• It might be a conflict when I save in the Visual Editor and the HTML Editor separately. But I saved the same posts in both and the output on the site doesn’t change.
• It could be I’m using the_excerpt() rather than the_content() to display the page, but I’m only using that on content.php, not content-single.php so it should be displaying properly.

I could possibly install a “Tiny MCE Advanced” plugin that might help fix the problem, but I seem to have this problem on MANY sites – both that I’ve developed and with themes I’ve downloaded. I just wonder WHY <p> is being replaced with ” and how to fix it.

Any help would be appreciated.