I'm mid-way through my first SHO project and I've noticed something odd with Sadr. It does show up in my Ha stack but even more so in my Sii:
ZWO 7nm Sii filter
SW ED80 DS-Pro
93x 180s (Stacked in Siril, processed in PS)
It shows up immediately upon the initial levels stretching. I've never had this problem with DSLR, so I'm quite unfamiliar!
I assume it's as a result of the ZWO filters but there are loads of possibilities, so wanted to check the wealth of knowledge on here!