Certain videos playing as "live"

[TheDreadPirate]

It looks to me like your transcode is simply not able to keep up with the stream. It starts off strong, but eventually drops to an fps just above 1.1 times the rate needed, before, presumably, dropping below the 1.0 minimum and ending the stream. You say you have disabled transcoding, but there isn't really a way to do that entirely. If the client device does not support the formats, and requests a transcode, the server will provide one. The only way to prevent that from happening is to make sure that all of the conditions on the client device (network speed, codec support, container support, etc) are all compatible with the source of the stream.

Ordinarily I would suggest making sure that hardware acceleration is enabled to facilitate transcoding when necessary, but since your server device is a Pi--and a bit under-powered for Jellyfin generally--that's not really an option here. You'll have to make absolutely sure that there is nothing about the source that would require the server to transcode the media for your clients. You should be able to look in your server log to see why the server decided that a transcode was necessary on the first stream.

Is it possible that the storage the transcode is being written to isn't able to keep up with the transcode?  Perhaps writing the transcodes to ramdisk might help?