Multiple accordion create error in updating pages

I am trying to create a page with multiple kadence accordion elements in it, each one with several panes.

If I use just one accordion item, I have no problems with it, but when I use more then one, when I click update it shows “Updating failed. The response is not a valid JSON response.” I googled that error message but no solution is relevant to mine. I tried on my online website and also on local copy.

So to solve the error I tried to convert them to HTML blocks to inspect what issue the block is having, but found no clue and when converted the block says “This block contains unexpected or invalid content.”

If I click on attempt block recovery, it comes back to normal, but it doesn’t save anyway, shows the same error.

If I click on resolve it shows me this: https://gofile.io/d/sd2EXE

Something breaks the block during saving probably, because I also tried to create a new page and use only there kadence accordions, and the same behaviour happens.

Kadence up to date, WordPress up to date, no builders installed, only gutenberg, no other third-party gutenberg plugin installed. Astra Theme.

Could you help me debug this? wp-debug also shows nothing when the JSON error occurs.