YouTube message suggesting wrong compression settings (Wondershare Filmora)
What that message likely indicates is that the MP4 produced by Filmora does not have its MOOV box at the beginning of the file. The MOOV box has metadata about the audio and video streams contained in the MP4.

Why this matters is that Youtube speeds up processing by breaking the uploaded video into segments, processing those segments in parallel, and then joining the processed parts into a whole video again. If the MOOV box is at the front of the file, Youtube is able to start creating the segments and dispatch them for encoding as the file is being uploaded. If the MOOV box is at the end of the file, it has to wait for the whole file to be uploaded before it can start processing.

A cursory search did not reveal how to get Filmora to place the MOOV at the beginning of the MP4.