Did you ever resolve this issue? I am curious. I have seen this issue with problems that use the AskSage method.
I only see the issue with Ubuntu 20.04, and only if the package libtypes-serialiser-perl is installed. It is not that package though, it is something that has changed with the perl JSON module itself I believe. If I install the perl module Types::Serialiser directly from cpan this also occurs.
This did not occur with Ubuntu 18.04.