From the title of your thread, I guess that, when you select 'Print' from an app that supports in-app printing, sometimes you get a menu that shows your printer and then everything is OK and sometimes you don't and there are no printers shown.
I've had a similar problem - but not really the same, so not sure if my experience is relevant at all - if it's not, just ignore me (most people do anyway) and I'll go away.
I have a printer that's not AirPrint compatible so I use the third-party app, 'Print N Share' (well, to be completely honest, its predecessor 'PrintCentral'). This app effectively makes my printer 'look' like an AirPrint-compatible printer, so it appears in the print menu of apps that support in-app printing.
Now, I sometimes experience the exact same problem as you do. After much experimenting (OK - fancy word for trial-and-error) I found that my ADSL router was occasionally changing the IP address of the printer, which confused the iPad - or perhaps 'PrintCentral'. If I forced the IP address back to the original address, no problem. Eventually, I managed to discover (good old 'trial-and-error' again) how to set up the printer with a static IP address.
OK - as I said - it's probably no help. In my case, there are several people in my house who have laptops that are constantly coming-and-going and this seemed to cause the router to constantly re-assign IP addresses. Additionally, I occasionally have to reset the router and, of course, it then completely re-assigns everything.
OK - I'll keep quiet now and go away and dig my car out of the snow...
Tim
snowy Scotland