I've run into this issue with my indexers lately where my Catalog Search Indexer will run indefinitely with a lot of backlogged tasks.
And if, and when, I edit any product or even add any new attribute without even assigning it to an attribute set this backlog will increase exponentially and will cause certain, if not most, products to disappear COMPLETELY from the frontend, but NOT from the backend. I had this issue the day before where I found my Catalog Search indexer giving this when I run the
Catalog Search | Reindex required | Schedule | working (952 in backlog) | 2022-03-08 15:33:26|
My indexers will be delayed for hours before being completed, which is probably why the products disappear.
Can someone provide some insight as to why that may be happening?