Search API with Application Permissions returns no results, Delegated permissions do

I've been experiencing this issue across the board, here in Australia too. Search results through application permissions is returning 4 results for a request with row limit of 10 for some, 0 for others. Running the same query as a user returning dozens of pages, 200+ results with a few refiners selected. Running queries only returning back titles are working fine. I think this is in-line with the symptoms everyone else is experiencing.

I don't think there is much more to contribute except for getting Microsoft to notice the issue. SP Search has been an extremely useful way to surface large data sets across many sites and lists. It will be a shame if we are forced to offload to a different medium to achieve the same results in a more reliable fashion for business-critical operations, without exposing a service account with no MFA in conflict with Microsoft's best-practice security recommendations.