We have seen this in the past, it is a nightmare problem but isolated it to being upgrade related.
Index structure in PG depends on the locale at install time and upgrades can lead to a nightmare sometimes.
https://github.com/docker-library/postgres/issues/582
If the reindex is not issued early enough, trouble can ensue. Some of our earlier PG docker upgrades did not run this… and some old installs sadly have a bit of a time bomb.
This is mostly resolved these days in the ecosystem but some pain remains.