It is usually a tif, since that is what I use after raw processing in ACDSee Ultimate. I haven’t really kept score on that count though.
I usually process RAW in ACDSee, then send images to the ACDSee “Edit” tab (layers capable bit mapped editor), and invoke Studio 2 as a plugin. This doesn’t happen when using Sharpen AI and DeNoise AI directly as plugins.
It also happens when I invoke Studio 2 as a standalone and invoke the plugins.