Having a Vertical split enabled, some emails you receive might not show the Subject line as the record snippets will take away all the space.
You can hide the snippets from the incoming emails in each folder Settings (choose the option: Hide snippets from threads):
Then in your Inbox, the snippet from the hidden folder will be available under the "+" sign:
This way you will see the Subject line of the email and the record itself will still show up in the email to its right:
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