Sparse indexes are not supported in stableAPI. When strict mode is enabled and an index hint wants to use a, previously built, sparse index the server reports back the following error:

planner returned error :: caused by :: hint provided does not correspond to an existing index

This is a bit confusing as the index itself does exist but is not available in strict mode. The decision needed here is if we should change the error message to indicate that the index is not usable under strict mode or we leave the error message as is.