Bhante @Sujato does have these notes in his Snp4.11 translation, and I believe he talked about this issue in this series: Seminar Series for Sutta Lovers: The Sutta Nipata (Atthakavagga)
“Without normal perception or distorted perception;
[Following Niddesa.]
“Na saññasaññī na visaññasaññī,
not lacking perception, nor perceiving what has disappeared.
[From the following verses we can infer that these enigmatic lines refer to an advanced state of samādhi, probably the formless attainments. These are not “normal” as they have no sense-perception or defilements; they are not “distorted” as they are free of hindrances; they are not the non-percipient realm; and they do not perceive what has disappeared, namely the rūpa or the sukha of lower absorptions.]
Nopi asaññī na vibhūtasaññī;
That’s how to proceed so that form disappears:
Evaṁ sametassa vibhoti rūpaṁ,
for concepts of identity due to proliferation spring from perception.”
[In MN 18, we have the sequence perception, thought, proliferation, then papañcasaññāsaṅkhā. This suggests that papañca causes saṅkhā, as per Bodhi.]
Saññānidānā hi papañcasaṅkhā”.