"Waving" accelerometer signal

I’m using Pixhawk 2.1 Cube Black. A while ago I moved from ardupilot to px4 firmware, but thereafter an issue with accelerometer data occurred.
I tested the sensor in elevator. Peaks showing accelerations at the start and finish of movement with static speed between. Logically, we should have flat line somewhere around 9.8 m/s^2 at static periods, and we do see it with apm (Z-axis acceleration to time):

But with px4 line of acc data is somehow waving (dont take into account odd x-axis integers, used it just to build plot):

What I’ve tried: reinstall firmware, change firmware version, recalibrate sensors using QGC multiple times, checked whether physical parts are damaged or nor etc.
Lost hope to understand what it is, cause have to small experience with pixhawk…

Anyone saw anything like that before? Will appreciate any thought or insight about it!

Wow this doesn’t look correct. Can you create a log from the Pixhawk Cube doing logger on and logger off in mavlink shell and then upload the logfile to logs.px4.io? Thanks.