New ingress-nginx versions introduce new validation rules for its annotations, which is breaking some tools using custom Ingress objects (like it did for the interwiki handled in T408570).
P84923 is a list of all tools using custom ingress objects with at least one annotation present, although not all of them are surely affected. In general there are two use cases, redirects and transparent proxying. The redirect case is known to be broken when using placeholders ($1) in the redirect target, the others I haven't tested yet.
(In theory all of this falls into the "using raw Kubernetes features is at your own risk", but I want to at least understand which tools are exactly affected before deciding to break things.)