Reusable Blocks – Disappearing HTML code on 4th/5th use

When I use reusable blocks in WP post editor, I copy paste the embed code into /shortcode format (I’ve also tested HTML).

The code works.

I save it as a Reusable block.

I use that block as a CTA 2x in the blog post.

Then, I use that reusable block CTA (which now has a little ‘lego block’ symbol over it), in 1-2 more blogs, using the block 2x each post.

By the 3rd or post post of using this block, the symbol beside the Reusable Block’s name, has changed from a ‘Lego block’ symbol, to a black box with white shapes inside.

When this happens, the reusable block no longer works.

I can go into Manage Reusable Blocks, click on the block that was just working 1-2 blog posts previously, but now, when I look in the code, the embed code that was previously there, is empty.

The code vanishes.

So I re-paste the HTML code.

But could someone clue me in on what is happening here?

Many thanks!

Example on this page: https://self-publishingschool.com/how-to-write-a-book/

>>This Smart CTA should be here in the post: (screenshot link) https://prnt.sc/14juekw

But it’s not… (see post)

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>>And if I go to the Reusable block, I instead see this…

(screenshot of code) https://prnt.sc/1443gh0

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>> (screenshot of another block this is happening to – sorry prnt.sc stopped working – this is a Google Drive screenshot upload)

https://drive.google.com/file/d/1E6UkBilvF_8kTD-74T1O3C_QTluxsue2/view?usp=sharing

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>> Code should look similar to this, but specific for this CTA.

https://prnt.sc/14445lo

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>>> What it looks like on a blog post when the Reusable block is working (unless this one quits before anyone can answer this….LOL)

It looks like this on a blog post:
https://self-publishingschool.com/how-to-make-an-audiobook-step-by-step-with-video

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Using WPengine.

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Many many thanks!

-Dee

The page I need help with: [log in to see the link]