Up until sometime in the last few days, the current version of Debian Testing (aka Stretch) was using a 4.0 Linux Kernel series. The 4.1 version has been migrated from Sid to Stretch. At this point in time, there are a few wrinkles.
Up until now, I was using a netboot from distribution for my pxeboot environment. With the migration of the kernel, this location, at this point in time, has files from 2015/07/18. This caused errors like:
"No kernel modules were found. This probably is due to a mismatch between the kernel used by this version of the installer and the kernel version available in the archive."
Debian Bug Report 7499991 hinted at a course of action. An updated netboot could be found from the d-i.debian.org site. After installing this, the installs once again work as expected.