Aquatuner pipe sensor triggering improperly

Did you check the contents of the aquatuner?  You might have a stuck packet of water that isn't getting cooled because the aquatuner isn't on long enough.

Therefore the other packet keeps looping because the aquatuner is FULL and won't allow any more packets in

@Neotuck  Yeah, the AT is empty, no contents.  There's 2 wide gaps after each packet in the loop, so if there was anything in there it escaped a while ago.

Then I don't know, personally I prefer to use shutoff valve to bypass aquatuners

But that doesn't mean your build shouldn't work

Is it possible the aquatuner is off before the packet reaches it?

It absolutely is turning off when the pipe vacuums, that's why the 3 gap exists.  You can't use a pipe sensor then add something downstream correctly with it activating.  If you want to empty the pipe loop only when it's hit the correct temperatures.  I can engineer my way out of it but the problem exists.

Upon further investigation, I'm finding out that ANY aquatuner + temp sensor pickup is behaving this way.  If you have 50C as your target, and a 49.8 has just passed through, it'll get absorbed by a 50.2 flipping the switch, and if a 49.9 follows it, the 50.2 skips the aquatuner. 

It would appear to avoid this, a pipe thermostat + cutoff + bridge/Aquatuner loop should handle the issue, but it seems overkill.