It’s been a while since I’ve printed but I think both my sidewinder and voron do this. I don’t remember having it after switching to abs. Painted on supports and wider extrusions helped a ton if I remember correctly. Good luck!

It could be a lot of things. Temperature is a big one, are you letting the bed heat up completely for a consistent amount of time before each print, could heat be impacting your measurements, some things measure different when heated a bit? You probably aren’t printing enclosed, but my voron for example expands upwards almost an entire layer over the first hour of printing. Is there an intermittent air flow that could be impacting how hot your bed really is? Have you verified there is no slop or backlash in your z lead screws and connections? I had decent results on my sidewinder using POM anti backlash nuts. Same for the stability of your measuring tool. Have you checked that it’s not z tilt from turning off the motors between prints?

Oh hey I kinda helped get this started in a very round about way! Nice to see the fluid integration, maybe if I do the mainsail one, someone else will do it a better way lol. I’ve not been printing much lately but set spoolman up a while ago on the pi running my voron and it’s been great.