Some emails not showing up on search index

Ever since I updated from iPadOS 17 to iPadOS 18, when I search emails, some of the emails are not indexed. So I have to scour all the emails. Even though the email is downloaded, it’s not indexed by searching.

It’s not just old emails that are not indexed, but some recent ones from no more than a month ago.

Below the results that are indexed, it says the following:

“Some results may not appear.

Mail downloads and organizes messages when iPad is locked, charging, and connected to wi-fi.”

But that doesn’t explain why the result doesn’t appear, because the email I’m looking for is already downloaded. I am sure. The update wouldn’t just remove the download.” The iPad is also connected to wi-fi, and it is charging.

I try waiting, but nothing happens.

Why would the update change this?