Actually the problems have been upgrading from that version. Either 20257 or the immediately previous build (but I suspect it was 20257) added A LOT OF CRUFT which has prevented my from upgrading to the latest build. Roughly 3GB of cruft due to Facebook, March of Empires, Candy Crush and some other pieces of dreck which I had uninstanned AND purged from my system previous had reappeared. This may not seem like much of a burde, but I run Insider Builds in a VM with a fairly small C: drive. New Builds seem to require 12GB free disk space on C:, and with this new rubbish, I was down around 10GB.
This is the first time in a long time I’ve had problems ugrading to a new Insider Build. I expect problems with unfinished software like this, but I don’t expect the reappearance of rubbish I’ve already cleared away. Also, this proved more of a chore than it had been the last time because of no longer being able to change permissions using icacls under C:\\Program Files\\WindowsApps. I had to add my Insider Build VHD as an extra drive for a Linux VM, run that Linux VM and use Linux to delete files from my Insider Build’s C: VHD. And, for all those skeptics agast at my doing such a thing, the Insider Build works just fine after having done this.