Originally reported and fixed by MDL-74193 it is happening again because of a regression caused by MDL-76583

Basically, the problem is that the new core_external\util::format_text method is setting to NULL itemids that are supposed to be 0, in particular, this line of code:

https://github.com/moodle/moodle/blame/9242f9619ae6fb3881dbbc0c96030acd65ea5892/lib/external/classes/util.php#L546

To fix it, we just need to remove these lines:

if (empty($itemid)) {
$itemid = null;
{color:#000000}}