Intermittent missing chunk ERRORS

All;

I am working with a client, they have an app that is running into error's like this:

SQL Error [XX001]: ERROR: missing chunk number 0 for toast value 44915477 in pg_toast_5321896

I thought it was a corruption / REINDEX issue, however I have run REINDEXon the index, REINDEX on the table and even a reindexdb on the database. Today they passed me another error (the one above) and once I was able to login I ran the same query the app team referenced and it ran without any errors. I asked them to re-run the query and they informed me that it now works for them as well.

I assume that if this were a corrupt index issue then the query would continue to fail every time.

Has anyone seen this type of intermittent index error before? and thoughts on where to look /how to debug this?

Thanks in advance