Some of my clients accept 4K streams with no problems. Other clients buffer an unwatchable amount even on 480p from the same server. Sampling all the way down

Some of my clients accept 4K streams with no problems. Other clients buffer an unwatchable amount even on 480p from the same server. Sampling all the way down to 480p is definitely odd behavior on a LAN--can't say I've run into that. Have you had much help from the usual spots? I'd be curious to help troubleshoot this sometime, sounds like an interesting nut to try cracking, or is it something inherent to the clients with the way they're decoding?