The fact that you can't record is probably because the OS, and therefore the app, don't detect any valid input.
Have you made this test : plug the cable and the source before launching any app, then launch any recording app and check if it's working, then launch Everyday Looper and see if the behavior differs. It should not as we are all slave of the OS input choice.
The phone expect a minimum load on the mic input to consider the input as valid, and depending on what you have connected the cable to, your experience may vary. For example, with the PRS GuitarBud (which is basically the same thing as your A/V splitter) some guitars are detected on a quite random basis.
More technical, and precise ^^, infos here :
http://blog.faberacoustical.com/2009/iphone/iphone-headset-input-options/.
Have you tried with a standard headset too ?