My experience is exactly the same as Isalterid in his Whimsical IPAD-Calibre/"content server"! thread (excellently descriptive title):
https://www.mobileread.com/forums/sho...d.php?t=131852
I suddenly managed to connect to the server via Stanza on my ipad this evening (I've not been able to connect for several weeks) - and then lost the connection again. I stopped and restarted the server in Calibre. This does not always work, but tonight it has.
Tonight I can reach the server by using its address - but this is not always reliable either.