ATtiny85 pulses its pins at about 10Hz after some kind of programming/wiring messup
I'm not an Attiny expert, but this sounds like the firmware that's running on the attiny is going haywire, possibly resetting the thing after a while or something. 

Doesn't sound like any "diagnostic" mode at all: MCUs don't tend to do such things – there might be dangerous things attached to their outputs, so wildly pulsing one's outputs is among the last things one would want.