Pressure increases with hot chamber?

I'm currently reworking my load because of this same issue but N565. I did all my load dev on virgin brass. Once I got to 2x fired I noticed velocity increase like you and once in a while a hard bolt lift. I had to back down to 59.2. I initially thought I wasn't bumping my shoulder enough as some cases I had to force close to fire. I resized a few today and shot. Well I ended up breaking my extractor today when I had to force bolt open.
 
Just started using a suppressor th7s year and have yet to run into that problem of finding pressure sooner with the can.
I had that issue a couple of times, but it could be me doing something. Now I assume the velocity loss and work the load with the suppressor on. It's never much but you still bothers me a bit.
 
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