I looked in /var/log/apache/error.log (Ubuntu location) and saw the following (slightly cleaned up after cut+paste) when tested with a Docker version running more-or-less the develop branch of WW. What it indicated is that this problem cannot be handled by the XML code needed to do the "inline" display of this problem, and is not just a matter of UTF-8 characters causing problems.
Error message for command: renderProblem
faultstring: Not an ARRAY reference at /opt/webwork/webwork2/lib/WebworkWebservice/RenderProblem.pm line 581.
End error message
[Wed Oct 07 17:21:56.368637 2020] [perl:error] [pid 77] [client 172.19.0.1:33102] [/webwork2/instructorXMLHandler] Error message for command: renderProblem \n faultcode: Server \n >faultstring: Not an ARRAY reference at /opt/webwork/webwork2/lib/WebworkWebservice/RenderProblem.pm line 581.\n \n End error message \n * in WeBWorK::ContentGenerator::instructorXMLHandler::content called at line 233 of /opt/webwork/webwork2/lib/WeBWorK/ContentGenerator.pm\n * in WeBWorK::ContentGenerator::go called at line 386 of /opt/webwork/webwork2/lib/WeBWorK.pm, referer: http://localhost:8080/webwork2/Madar_devel/instructor/sets2/035-hw03-additional-problems/
I hacked at the code a bit, and the XML conversion is failing to handle a
Value::Matrix as the value of
correct_value inside an AnswerHash object. It seems that we are running into limitations of the current support WW has for rendering problems via XML. That also implies that it probably cannot be handled by the xml2html system for embedding problems in a web page, as it would also need to undergo the encoding to XML which is failing.
It is possible that the XML support code could be extended to handle Value::Matrix with special code, but that is a project to consider in the future. I've created a GitHub issue about this.
Out of curiosity I tried out this problem in the new Rederly standalone renderer, and it renders fine there.