Can't figure out why 430exii will only do TTL and not E-TTL?

So I randomly (it seems) will not be able to get my 430exii in E-TTL, and I can't seem to figure out why it happens, it will just switch from TTL to M. It happened on the hot shoe at a wedding last night, and then seemed to go back to E-TTL on it's own in about 5 minutes, and it happened again today when testing out my new Pixel King triggers.

I'm sure this is a simple thing that i'm overlooking but I can't seem to figure it out, any thoughts?

This usually indicates a flash to camera connection problem
Dirty contacts or loose connection.

If the camera has gone into sleep mode, the communication between the flash and the body is inactive, which could be causing the flash to switch out of ETTL mode.

With my Metz 54MZ, when I turn on the flash it is in 'TTL' mode until I turn on the camera or slightly depress the shutter button after it has gone to sleep, when the flash switches to 'ETTL'.