Hi,
I'm having the same issue, Been through several, rounds of revoking then reapplying the "Trust this device" options, weirdly, it would allow me to see Web Inspector Content up to the point I would enter my passcode on my phone and then, as soon as I did my device would disappear from the develop menu.
I don't have solid, reproducable proof yet but I saw in some other thread that theres an issue with the Charge status. So if your phone is at 100% charge (which being connected via the usb cable is quite likely) you won't see it listed in the Develop menu, but this morning with my phone at 46% charge there it was.
That said the experience is still very erratic so it might not be as simple as that.