In T97928#1296058, @Lokal_Profil wrote:

This issue popped up recently for the Wikidata:Menu Challenge where we have a fixed list of entities. Once some of them got merged (and thus redirected) wbgetclaims fails whereas wbgetentities (to get labels) goes on happily.

Even wbgetentities loads the entity enough to get the label so most users would expect getting a claim of the same entity to work in the same way.

Example: https://www.wikidata.org/w/api.php?action=wbgetclaims&entity=Q6449034&property=P31