[landing page] unable to save custom HTML code

Your software
My Mautic version is:
My PHP version is: 7.4.18
My Database type and version is: mysqli / mysqlnd 7.4.18
cpanel/centos os 7.9

Your problem
My problem is:
We create a template using beefree.io (pro version)
When exporting the html and saving in custom html in the builder, we only this line of code showing.

<!DOCTYPE html>"

These errors are showing in the log:
There are no logs

Steps I have tried to fix the problem:
Tested with different HTML outputs, all trigger the same issue.
However, if we build a custom email, the builder works.
We have tested this on a different server environment and we are able to save the template without issues. We are wondering if the server setup may have something to do with this, or if we are perhaps missing a module or something like this. But not sure what.

Any help would be appreciated

What is the first line of code you try to insert into the builder? (Is it the GrapesJS Builder?)