I have used Paterson Orbital for more than year now, mostly with success.
However, I have noticed that with XTOL 1+1 and Hp5+ 4x5 sheets I got some uneveness.
It's not very predictable, but when it occurs, it always happens near the edges of dense and low/midtone areas.
Like the developer from the low tone areas had "leaked" to the denser areas. Something like you could expect with a stand development.
But in this case the movement is constant and quite fast (the developer travels over the film once in two seconds, 30 times per minute).
So I am wondering does XTOL behave somehow differently than other developers that I use with Orbital (like Pyrocat-HD 1:1:100 and Rodinal 1+50 & 1+100)?
In the attached picture, the effect is visible on the sky, around the roofs.