Based on my testing the 'reboot --eject' option, doesn't actually eject the disc after installation on Hyper-V (Windows 10). I have had an issue with this on other hypervisors (vmware/qemu) but I suspect those machines didn't have the DVD drive configured as first in the boot order, so failing to eject didn't matter.
This is a regression with the RHEL 8 beta, as the problem was fixed by issue #1595799 and the installer is still working properly for RHEL 6 and 7.
*** Bug 1578307 has been marked as a duplicate of this bug. ***
This bug will be fixed in RHEL-8.2 as part of bug 1805405.
I'm closing this bug as a duplicate.
*** This bug has been marked as a duplicate of bug 1805405 ***