In current point I can’t advise because I don’t know what you are doing and how. Blocks are just html code, if you copy them correctly then they will be correct. I guess you have wrong sanitisation of code.

please, note that your support is expired so we cannot help in such questions. 

You can reopen when you will have active support if you still need help

Hello, I am currently utilizing your theme on my WordPress website and attempting to copy a post and create a new one using Python and the WordPress REST API. The issue I am facing is that when I make a post request, the building blocks that were present in the editor in the copied post are missing, leaving only raw HTML. Is it possible to retrieve these building blocks and re-add them to the newly created post via the WordPress REST API?

It is about these 2 pages:
New page:
https://dehetbeste.nl/test-15/

Old page:
https://dehetbeste.nl/template-single-review/

I have also added 2 attachments where one is the editor of the original and the other is the editor of the newly created page. You can see that the list of blocks has disappeared.