I get that alot with my TV (Panasonic 42AS650) but after a few seconds it will find both my media servers - Mezzmo & a Synology NAS.
It's as though it needs that little bit of time to make it's network connections properly & then re-queries successfully.
In the Media Server settings there's a "Server advertisement interval" - maybe in your network this needs to be lowered from what I believe is the default of 86400 secs (24hours).
I'm sure Paul will be in soon to give you the right answer.
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