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