Our installer includes a kernel extension, which is loaded at the installation to make sure the "System Extension Blocked" dialog is shown to the user. On a beta version of High Sierra I did see this dialog, but on 10.13 (final) it did not show up. The allow button in the preferences is there as expected.
In the install.log I can see that the kext has been attempted to load as expected:
this is the output of "sudo kextload /Library/Extensions/CmUSBMassStorage.kext -v":
./postinstall: /Library/Extensions/CmUSBMassStorage.kext failed to load - (libkern/kext) system policy prevents loading; check the system/kernel logs for errors or try kextutil(8).
this line is written if the returned status code is 27:
./postinstall: Kext has to be approved by user!
Any idea why the dialog could be missing?