Here's one repro:

1. Enable Switch Access. By default it should be configured so that Volume Down highlights the next item on the screen and Volume Up selects. Ensure this is working, for example in Settings or in the Home Screen.
2. Open Gmail
3. Select Compose
4. Use Volume Down to move to the Subject text field and press Volume Up to Select. It gets focused.
5. Now use Volume Down to move to the body (Compose Email) text field and press Volume Up to Select.

Expected: the field should focus and the virtual keyboard should pop up if it wasn't already.

Actual: the field does not focus

This can also be reproduced with Voice Access, see b/37641670 - but that product might not be available to everyone.

You can reproduce this with almost any app that has a text field in a WebView. The problem happens when focus is initially not in the WebView at all, and then you try to click in a text field in the WebView. If focus is already somewhere else in the WebView, focusing the text field succeeds.