I am already with this problem for more than 3 weeks now and is driving me insane.

Trying to create an monitoring via HTTP Agent
Version of Zabbix: 4.2.1
Request Body Type: XML Data
Not Converting to Json, but already tried this option
SSL verified peer/host off but already tried this option on
No HTTP Proxy

looked everywhere what this error means (really) and could not find

Already put the log debug until 5, no luck also

if the return has an iso-8859-1, even with a preprocessor in place, gives an error

Preprocessors I tried to convert the characters, the test of the preprocessor works, but the error persists

==> return value.replace(/ã/g,'a').replace(/ç/g,'c');
==> return unescape(encodeURIComponent(value));

Preprocessors I tried just to extract part of the return (just to confirm the preprocessor was not working)

==> ^(?<=\<ns2:status>)(.*?)(?=\</ns2:status>)$
==> (?<=\<ns2:status>)(.*?)(?=\</ns2:status>)

the logs show that,even with the preprocessing rule, when the ISO characters are not there, the data is inserted in the db, and processed, if not, the error appear right at the moment that the DB is supposed to insert the data and it  is right away discarding the data, like the rules are being completely ignored.

there is 10 preprocessors processes started