Odd AI behavior

[Ghost42]

At one point on the route the AI will stop at a trackmark and not move until the train in front has passed the next trackmark. There are two permissive signals in between.
I am sure I am not alone with this bottleneck, anyone have an explanation?
Rog TS12

 

[shaneturner12]

I had a similar problem previously - do you have any junctions/turnouts between the two points?

Shane

 

[Ghost42]

I had a similar problem previously - do you have any junctions/turnouts between the two points?

Shane

There is one just before the second trackmark, the trackmark could be moved but I would prefer not to if possible.
Edit:
I moved the trackmark and this resulted in the same behaviour but noted there was a M.I.N inline, put in a bypass now all is well!