hl7.org has some redirects in place so that users can dereference codesystem urls that are defined in the specification (i.e. "internal" FHIR codesystems).

However, these are still resolving to R4 where they should now be R4B (or "latest"):
http://hl7.org/fhir/abstract-types
http://hl7.org/fhir/account-status
http://hl7.org/fhir/action-cardinality-behavior
...

Not sure if its related or not, but at least one doesn't redirect at all:
http://hl7.org/fhir/clinical-use-definition-category

https://chat.fhir.org/#narrow/stream/179165-committers/topic/R4B/near/287344117