Extruding snaps back I'm using blender 2.8 for over 2 weeks now.

If I extrude a face, it snaps back into place. But only when the extrusion is under 0.200 meters.

I did check the "snapping" setting, but its not that.
Maybe you have automerge turned on, or with a too high threshold.

Turn it off or reduce the threshold in the Tool tab of the 3D Viewport sidebar