by boot.img from "current release" do you mean...Actually, that won't work, since you require root to be able to install it to the inactive partition. At this point, you need to fresh-install Magisk: Extract boot.img from the current release, use Magisk to patch it, boot from the patched image, and install Magisk directly. Once you've done that, you'll be able to go back to patching the inactive partition after OTA updates.
1) the latest OOS firmware we installed before installing LOS?
OR
3) the boot.img from the LOS zip file?
Thank you!