Might be a weird question!
I have brewed, with a friend, 6 batches of beer so far. An IPA, then a Stout, a Saison, a Doppelbock, an Baltic Porter and finally, the same IPA. All grain, always.
Of all these, only twice we had that weird white film over the beer in the carboy, in the second fermentation. It comes with a few white bubbles. there are some lines of that white that are traced, a little bit like a spider web.
Either we got infections in both, or... the dry hopping creates that? Is that possible?
At least I know now that even if it's an infection, I just bottle the beer underneath the pellicle :)
EDIT: Here is the picture