Question about YT-DLP and a mess .part-frags

So I'll fully admit this is probably user error and not due to any bugs with the software. But I've been on a bit of a tear lately utilizing YT-DLP to download videos from YouTube. Now I'm not a stranger to this process, I'd used Youtube-DL successfully for years now. But I did recently take advantage of using it in conjunction Aria2c with the understanding that it would give me a bit more of a boost . Well...

I don't know if it's YT-DLP or Aria or my NAS or my Internet connection, but I went through to organize these downloads and found TONS and TONS of video files ending with ".part-frag###." There are thousands and thousands, and upon a cursory glance, seems to affect hundreds of video downloads. Each folder has dozens of these files and if it doesn't, it has split mp4/m4a. Rarely does a folder seem to have one clean video file like I would expect. I skimmed through and there seems to be finished files amongst the mess that seem to play fine, I can't be 100% sure though these files are as complete as they should be (surely the part-frags exist for a reason).

So firstly, what program or setting is causing this plague of fragments? Secondly, is there anything I can do to resolve theses files at this point? Yes, I can delete all the frags, but that doesn't give me any comfort in the integrity of whatever video file remains (and it won't solve the problem for future downloads). And as I archive to a txt file, I can't just re-download as YT-DLP considers them downloaded (I've tried redownloading to see it forces a re-check and cleans things up, but no dice). Is it just refusing to merge or delete for some reason?