This is the first OTA I've received never got any of the other ones. That's the weird part. I did back ups and had recovery files on my pc before trying the unmatching kernel and firmwareUsually bootloader unlocked devices are blacklisted for OTAs indeed. But there were always some reports of very few lucky users receiving OTAs, despite being unlocked.
If you want to update you can restore stock boot.img, dtbo.img and recovery.img from stock fw and the OTA should install fine for you. (I guess)
Or you wait for the full firmware.zip to be available. (that’s what I usually do)
Keep in mind, flashing a kernel based on a kernel source not matching the current firmware source, can potentially lead to issues as well.
I'll wait for the full update because that's what I've been doing so far and I'm used to that way with twrp and root.