I recently upgraded to the latest windows preview.And after the upgrade did a complete reset and restored the backup. only problem is the network will automatically turn off(Flight mode). And i Have to restart the phone everytime to get the network back Nothing else helps.... I'm using a microsoft lumia 640 and is it possible to revert to win 8.1 by any chance???
You say that you are using "the latest windows preview" and your title says "10.0.10586.36". As of 5th February 2016, the latest is 10586.71 (Slow Ring), as announced in the Windows Experience Blog.
First, if you have still sometimes access to the network, check for updates. If you are in Slow Ring, you could also try the Fast Ring.
It is also possible to revert to Windows Phone 8.1 by using the Windows Device Recovery Tool. In that case, don't forget to make a backup of your files first, as it will erase all data.