Since this bug is triggered by the Separator Block (``), the issue is likely a conflict between your WordPress Theme and the Gutenberg Editor. It's treating the horizontal line as a "Read More" tag or a content-breaking error.

Here is the "bench-tested" way to fix this across every post on your site:

1. The "Left-Brain" CSS Fix (The Quickest Way)

Often, the theme has a "demented" CSS rule that tells the browser to hide everything following a specific class. Go to Appearance > Customize > Additional CSS and paste this:

.wp-block-separator {
    clear: both !important;
    display: block !important;
    visibility: visible !important;
}

/* Force the following elements to show */
.wp-block-separator + * {
    display: block !important;
}

2. Check for the "Excerpt" Bug

Some themes are programmed to only show the "Excerpt" on the main page. If you haven't defined an excerpt, WordPress looks for the first "break" in the text-and it sees your Separator as that break.

• The Fix: Go to a post and check the "Excerpt" box in the right-hand sidebar. If it's empty, the theme might be cutting you off at the first sign of a block it doesn't like (the separator).

3. The "Conflict" Test (Investigation)

To see if it's a "Cowardly" plugin or the Theme itself:

• Switch Themes: Temporarily switch to a default theme (like Twenty Twenty-Four). If the post suddenly appears, your current theme's content.php file is broken.
• Check "Optimization" Plugins: If you use a plugin like Autoptimize or a "Lazy Load" script, it might be trying to "clean up" the code and accidentally deleting everything after the separator because it thinks it's a comment. Turn these off one by one.

4. The "Screwdriver" Method (PHP Fix)

If you're comfortable with the functions.php file, you can force WordPress to stop treating blocks as breaks:

add_filter( 'the_content', function( $content ) {
    return str_replace( '', '<hr class="wp-block-separator">', $content );
}, 9);

What this does: It intercepts the "Machine" code before it hits the browser and converts the "Buggy" Gutenberg tag into a standard, "Human-readable" HTML horizontal rule (<hr>).

The Reality Check

The fact that a simple line (---) is "castrating" your entire archive is the perfect example of how fragile the Digital Ark can be. You've built the content with Inspiration, but the Seagulls (the code) are failing to deliver it.

Would you like me to look at the specific name of the WordPress Theme you're using to see if this is a known "bollocks" error with their latest update?

As the code is identical and it's still cutting off the post, we are dealing with a "demented" priority issue. WordPress is likely running its own "castration" logic (the the_content filter) after your fix runs, or the theme is using a different function entirely to display the post.

The "Screwdriver" Fix: Increase the Priority

In your add_filter on line 197, you have , 9 );. In WordPress logic, a lower number runs earlier. If the theme is breaking the post at priority 10, your fix runs at 9, fixes it, and then the theme breaks it again right after.

Change line 197 to a much higher number (like 999): }, 999 );

Why this might work:

• Priority 999: This tells WordPress, "Wait until everyone else (the theme, the plugins, the 'Monster') has had their say, and then run my fix at the very last second."
• The "Seagull" Effect: If the theme is using a custom function like newsup_content() instead of the standard the_content, your filter is shouting into an empty room.

If that doesn't work, try this "Brute Force" CSS:

If the content is actually there in the "guts" of the page (check by pressing Ctrl + U on the broken post and searching for the hidden text), then the "Separator" is just triggering a CSS "Display: None" bug.

Add this to your Appearance > Customize > Additional CSS:

.wp-block-separator ~ * {
    display: block !important;
    visibility: visible !important;
    opacity: 1 !important;
}

The Logic: This tells the browser: "I don't care what the theme says; if it comes after a separator, show it."

The Reality

The Newsup theme (I see it in your file path) is a "Magazine" style theme. These are notorious for being "cowardly"-they try to be too clever with excerpts and separators, often breaking the "Inspiration" of the post just to make the front page look pretty.

Does the text appear if you view the "Source Code" (Ctrl + U) of the live page, or is the text physically missing from the code entirely?