I don't know whether you are experiencing the same or a similar issue as that which has been discussed in the "AXE I/O SOLO amp out problem" thread (also in this "Interfaces & Controllers" section of the forum, but you might want to check out that thread.
The first thing you should do is try to ensure that your AXE I/O firmware and the Control Panel app are both fully updated.
Then, I have had some issues with my AXE I/O that seem most readily addresses simply by cycling the power -- i.e., turn the unit off using the power switch on the back, waiting 30 seconds or so, and then turning it back on.
All that said, it seems to me that there do seem to be some issues (?) with the Amp Out jack on AXE I/O devices. No matter what I do, the signal coming from it always seems to be at least -18 dB or so lower than I would have expected.