Specific movie will not download or play from iTunes (error -50)

Beyonce's Lemonade movie will not download or play on my Macbook Pro (OSX Mojave). Other movies download and play just fine. All music works. It's just this one specific title.

In detail: it downloads just fine up until the very end. Once it's ready, it reports that there's been an error (-50). If I hit play on the file, it thinks for a while, then just closes the player.

I was able to watch about one fifth of the movie earlier today before it just stopped playback. Now it won't even start. Two additional copies of the same movie had appeared in my library.

Things I've done:

• Logged out of iTunes, logged back in again
• Recreated my iTunes library (this got rid of duplicate entries of the movie, which had also appeared in the library)
• Deauthorized & reauthorized my computer
• Updated OSX
• Restarted my computer, obviously
• Deleted all local iTunes media, emptied trash, redownloaded everything
• (Movies substantially bigger than Lemonade's 2.5 GB work just fine)
• Manually deleted the partial downloads folder's contents (which indeed do show the incomplete download for the movie)
• Tapped through all the options under "advanced preferences" in iTunes; cleared caches, reset tokens
• Verified that it's not an account problem; the movie downloads and plays just fine on my iPhone
• Verified that there's plenty of space on the iTunes HDD (in excess of 200 GB)
• Tried three different networks, so it's not a router or firewall problem (unless there is something on the OSX I'm not aware of)
• Thought of any software I might have that could mess with the download. Can't think of anything, and again: it's just this one movie...
• Wasted over four hours tonight on this

Any ideas? What might I have missed? To me it seems likely that either the source file is corrupt, or that there's something exotic iTunes does to this specific file. Do some movies use a different kind of copy protection? Or something?

I've watched the movie, downloaded through iTunes, before. It wasn't on this same Macbook, but an identical model and using the same Apple & iTunes accounts.

I don't want my money back, I just want to watch the movie I bought with my friends.