Curiously, if I start a download on mobile data, and then re-enable my wifi the download swaps to wifi and then completes quickly. It doesn’t seem to let me /start/ new downloads on local wifi but seems happy to resume them…
“DNS rebinding protection”
Put the domain name plex.direct onto the list of exceptions from this protection.
(if your DNS resolver or router actually provides such a setting)
I am not familiar with that router, so I can’t say anything definitive.
But if it doesn’t provide the required configuration menu, and you are also not able to replace it with a different router, then the answer might be Yes I’m afraid.