KMail 5.4.2/Fedora 25 very unstable

  I upgraded to Fedora 25 with KMail 5.4.2 this weekend and KMail is 
  very unstable. Simple things like scrolling through a message or 
  resizing the messages pane cause it to lock up or crash. My
  View->Message List->Sorting sessions are never saved. A mysqld
  process I assume is used by Akonadi (I don't use MySQL for anything 
  else) is constantly writing to disk. 
  
  I have run akonadictl fsck and vacuum. I do not have any problem 
  retrieving or reading messages unless I have to scroll them.
  
  I've Googled a lot and read bug reports but I find nothing that 
  relates to my situation. What could be going on? Right now KMail is 
  barely usable.