FFMPEG Python: Encountered scale(1920, 1080) with multiple outgoing edges with same upstream label None; a `split` filter is probably required

Here is the code in question:

for comment in thread['comments']:
 commentClips += fragmentConcat(comment, filePrefix)
 
 staticClip = ffmpeg.input('assets/static.mp4')
 commentClips.append(staticClip
 .filter('setsar', 1, 1)
 .filter('scale', 1920, 1080)
 )
 commentClips.append(staticClip.audio)

This code generates the following error:

ValueError: Encountered scale(1920, 1080) <6adb028f8ef5> with multiple outgoing edges with same upstream label None; a `split` filter is probably required

I have tried using only the video part of the input for the first call (e.g. staticClip['v'].filter...), and I have tried using the split call as suggested (e.g. ffmpeg.input(...).split(). Nothing has worked. What is the issue, and how can I rememdy it? Thanks.