Stability check issue during phase starting with 0 degree

Hi! 

I'm trying to design buffer amp for specific application, so I want to check stability such as phase margin using an instance 'iprobe'(actually it doesn't matter to use ac simulation). However, the loop gain phase plot of the circuit starts with 0 instead of 180 deg and it's unexpected plot. I think it could be related with positive feedback or multi loops, but I'm not sure about it. The transient result of the circuit works well, but I want to check the figure of phase. Could you please help me? How can I make it clear?

Thanks.