List items with Manged Metadata stopped showing in parent tags

Question

I am using managed metadata in SharePoint 2013. This morning, with no known changes on the site, it started working different. Here is some dummy data to match my structure.

-Project A
    -2015
        -Notes

I have list items that are tagged as Project A:2015:Notes. The items tagged as such used to show up in all 3 levels as we expected.

However, starting this morning, users are only seeing list items at EXACTLY the tag level that is specified, nothing higher. In other words, they see the items when navigating to Project A -> 2015 -> Notes, but NOT Project A -> 2015 or just Project A.

Has anyone else run into this issue?

We are only seeing this in first of our three environments that are configured pretty much identical, the only difference being the problem environment has a lot more items.

15,000+ items with the list view item threshold set to 20,000. I know increasing that value is a whole separate discussion but thought I should point it out.

Answer 1

I could not find anything helpful in the ULS logs.

I ended up running iisreset on all the servers in the farm. Then I went back to the site, and the items started showing up in all levels of the hierarchy again.

If anyone finds the true cause and way to fix this without an outage, please let me know!