403 error is generally an expected response when recovering videos. The way m3u8 lists work is that they point to a list of video files and your video player plays each segment that the list references 1-by-1. Since you said you’re trying to download deleted vods, it’s likely that the m3u8 list is still available, but twitch has deleted the actual video files it is pointing to, hence the forbidden error.
You might be downloading a muted segment. Vods may have some parts muted for copyright or other reasons. The URLs for the muted segments are different from the default (unmuted ones). If you try accessing the unmuted segment that is supposed to be muted, you will receive a 403 error.