New Covid strain evolved during a chronic infection in immunocompromised patient

This makes sense.

A person harboring the most replication of a virus is more likely to produce a prolific strain.

An immunocompromised individual is also much more likely to harbor other viruses that can share genetic material with each other when replicating.

If any human body in the world can be predicted to produce a radically different new strain, it's one whose body doesn't suppress viral replication.