Pixel 4 XL: after 8/5 update, K9 cant get mail

Hi. I bought a Pixel to keep up to date with updates, now a problem popped up today after updating Android 10 to the 8/5/20 security update. I can no longer get mail from the POP3 server - It just sits there spinning for a while, then stops quietly with no mail. I tried installing the latest Beta over 5.6, but still no joy. Help!