Alpha Glow effect makes .png file blow up in size.

I have used this effect hundreds of times with no issue, but on this new project, this weird thing happens (and not all the time):

I add Alpha Glow to a .png file that is an overlay. Most of the time, no problem. Most of the time in this project, no problem.

Sometimes, it makes the .png file blow up in size (even though it doesn't show it on the Effects Control percentage). (These are not all the same .png file, but they are all the same size and made the same way.)

Add the Alpha Glow - ..png file blows up.

Undo it - .png file stays the appropriate size. 

Add the Alpha Glow - .png file blows back up.

I try deleting the .png file and dropping it back into the timeline and rarely does it work. I want all these overlays to be consistent, but I can't when intermittently - and never before, only on this new project - the file to which the Alpha Glow is applied gets blown up in size. 

It's frustrating because it shouldn't happen. There's no reason for that to happen. I tried some of the fixes I found online, but has anyone experienced this before?