This has been going on for over a year now. No matter what plane I fly or what tweaks I make to video I get occasional freezes every five to 10 minutes. I've never been able to replicate a specific event that causes it. I've tried disabling all unnecessary processes. To eliminate third party plugins I did a vanilla install of 10.51 with no plugins, scenery, or aircraft loaded. The problem persists even with the stock aircraft.
I have observed CPU usage from the sim dropping to 0 when this happens and as far as the sim is concerned it reports frames drops from 40 to about 20. Disk usage and memory don't seem to be affected when the event happens. In reality frames are less that 1 per second. It is as if the sim gets frozen in time.
This was happening on my DVD version as well as my recently upgraded digital version.
With a dozen other sims and hundreds of games (sad I know), only X-Plane is having these issues.