You appear to be using the Testing Framework.
When I chase through the code, it looks to me as if there underlying code deliberately carries around two versions of the text, one with rich text / hyperlinking, and one without.
I did not manage to quite follow how which one gets chosen in toolbox/matlab/testframework/unittest/core/+matlab/+unittest/+internal/+diagnostics/TableDiagnostic.m -- I suspect it might be an implicit get() that is activating the choice.
The relevant code makes use of the built-in matlab.unittest.internal.richFormattingSupported which is undocumented and cannot be looked at.
I speculate that you might be able to turn off the formatting by starting MATLAB with -nodesktop or perhaps even -nojvm .