i've experienced this same exact issue for quite some time now, sometimes videos upload fine sometimes they don't. brave on PC w/VPN, clearnet, switching servers sometimes fixes it but idk if that's because i changed IPs or if it just naturally fixed itself.
sometimes it gets stuck at 100%, sometimes it "uploads" but you can't insert and have to refresh, revealing it wasn't actually uploaded.
once when it got stuck at 100% i checked network activity and it was double uploading for some reason. even when the upload goes through sometimes it still double uploads, bizarre.
and then sometimes uploading slows down immensely halfway.
i can't pin down any rhyme or reason to it, it seems completely random.