Mail Inbox on iPhone won't scroll past current screen (most recent email headers)

Today, my mail inbox on my iPhone 13, iOS 18.5, won't let me scroll down to older emails than the ones seen on the current screen (from today). I can see many more (older ones) in my inbox on my iMac.

I can scroll down through all other mailboxes (folders) on my iPhone with no issues.

I have nearly 50 GB of storage available.

Quitting and relaunching Mail and rebooting the iPhone did not solve the problem.

Any ideas? Thanks!