I remember running into this issue a long time ago. I think it's an inherent problem with box2d at low speeds.
Iirc it can be mitigated by using higher resolutions/sizes and downscaling, resulting in relatively higher speeds while visually remaining the same.
Apologies I am quite new to Construct, I don't really understand what you mean. I have created a quick project with the values and resolutions that I am currently using. I hope this can make it easier to understand the issue I am having
https://www.filemail.com/d/mdeaqxeljxnwdes