Yes, I've had this problem with my M1 MBA repeatedly. The system policy warning occurs, but nothing appears in the Security & Privacy pane. Literally the only way I've found to load a new kext is to boot into macOS Recovery, re-enable the Full Security policy, reboot, try to load the kext again, then shutdown and boot back into macOS Recovery, enable user-managed kext mode, reboot, Allow the kext, and then reboot again.
And yet after all that, despite confirming that my kext is loading and taking effect, the KextPolicy database itself still doesn't list that kext bundle ID as being allowed.