Welp... i'm trying to understand why you are so mad that everything is working as expected. You are aware that renaming files/directories will lead to inexistent paths.
Either you're indiscriminately renaming stuff like a psychopath or there's something misconfigured with your NAS, but I think it's the first option.
You should stick to a single torrent client if you download from multiple devices and check if your server is available 24h or if there's any kind of operation happening that could lead to its unavailability.
Not only that but you could also swtich to a torrent client that will stop torrents with missing files instead of redownloading them. qBittorrent is a good option, if you rename stuff directly using the operating system, or for some other reason the file or entire path become unavailable, the torrent will stop and you'll receive an error warning within the app.
Additionally, if you need to move files or folders from one directory to another you should always do it using the torrent client instead of using the operating system file explorer. This is important regardless of running a NAS or offline storage, always manage your torrent data using the torrent client.
Additionally, if you use multiple devices, don't ever try to have more than one client seeding the same torrents if the torrent app data is stored offline.
You can install a portable version of the torrent client within the NAT as well, so whenever you rename something using the client it won't lead to stuff becoming unavailable in other devices.