Hysteresis and mode jump in oscillators

What does authors mean by that? In microstrip oscillators, how it can operate in hysterrsis mode? Second question is about mode jump. Is it jump in operating point (class a jumps to c) or frequency jump?

Questions about an article without linking or quoting the content are somehow difficult to answer, isn't it?

I'm sure the author is talking about frequency jumps. It's easy to get multiple possible oscillations frequencies ("modes")with a microstrip resonator.

about hysteresis - you don't want it!

I have found it often comes about by micro-resonances in your bias tees surrounding the active device. try De-Q-ing them