Note 9 Pro users in this thread who replaced the persist.img have L3.Well, that means that the L3 level was not caused by overwriting the Persist partition, but it's probably a matter of ROM itself.
DRM Info on RN9Pro with replaced Persist.img shows the same things as on my second phone, Mi Max3, where I didn't overwrite Persist.img.
Note 9 users in this thread who didn't replace persist.img still have L1.
I'm still on 11.0.4 with L1, but there's at least one user here on 11.0.5 with L1, (and he didn't replace persist.img).
You should probably remove those steps from your guide, at least until it can be proved to be safe.