I've had this issue for years. I can only find one thread on the internet mentioning it. See attached image for an example of how my property manager always keeps expanding slowly to the right as I work throughout the day. I've only seen one potential explanation / solution involving an issue with rulers displayed in drawings. My property manager expands in both parts, assemblies, and drawings no matter what I do to prevent it. I'm also on a brand new laptop with Solidworks 2021