For some of my SQL questions I get frequent timeouts although sometimes they load in a few seconds (for some reason they load when I open the editor)… Also when they do load at some points the result would disappear to show again the timeout message. This happens for questions that reuse results from other saved questions/models.
Do you have query caching enabled?
I do 
Does the timeout issue get more consistent (consistently worse) if you turn off query caching?
What database are you using for your app database, and what database are you querying where you see the timeouts? Specify if the database(s) are remotely hosted (i.e., in the cloud). Also, what Metabase version are you running and what are the specs of the Metabase server?