MacOS Catalina Mail side preview stopped working

Today I opened mail and found that the side preview was no longer working. If I disable the feature in View, I get the bottom preview, but if I enable side preview the bottom preview goes away and I do not get a side preview.

I have restarted mail. The results are the same. Is there some other option I need to enable to get this to work.

A family member was using the mail app earlier. Not sure if they did something to cause it to stop working.