Body of email not showing up - viewing window is blank

Hello,

I just upgraded to Yosemite only to start having immediate problems with mac mail.

The program opens, and I can see all the emails listed in my inbox, but when you select one - you do not see the body of the email

in the viewing window to the right. That window remains blank. The only way to see the email is to DOUBLE click on the email in the list,

then another window pops up and you can read the email.

This is random. I can reboot and it will work properly....or it won't.

Wha