I'm sorry about the presentation. That's awful to hear.
We do have an API to delete documents: Documents API | App Search documentation [8.11] | Elastic.
This takes a JSON array of strings as document IDs. Does that work for you? How many documents are you trying to delete? Everything in the engine? I'm not sure about the limits on the number of documents you can delete with that API actually, but as a warning, if the documents are large or you're trying to delete a very large number of documents, that endpoint may not be very performant.
I'm surprised with the original error you're receiving, though. Are you able to reproduce this error in a consistent way? Are you checking the responses of the delete API calls? Curious to know more about this. I wouldn't expect the records to exist in the index still. Artem mentioned:
It seems more likely that isn't something wrong with the deletion side of things, but I'm interested to dig further.
Best
Brian