This relates to the jsonld file (eg https://github.com/prefixcommons/biocontext/blob/master/registry/go_context.jsonld) used for CURIE <-> IRI conversions.
WB:WBGene00006575 is translated in http://identifiers.org/wormbase/WBGene00006575 which used to redirect to the real WB page https://wormbase.org/species/c_elegans/gene/WBGene00006575#0-9f-10.
But this IRI (http://identifiers.org/wormbase/WBGene00006575) doesn't resolve anymore to a valid identifiers.org pattern. After double checking, the correct IRI would now be https://identifiers.org/WB:WBGene00006575.
For uniquely identifying resources, it doesn't change anything (our past IRIs haven't changed), but for resources that were relying on identifiers.org IRI to resolve and link out to actual websites, this is a breaking change and side effects would have to be investigated.