I'm experiencing this too. My guess is it is because I have unsaved changes in another instance of the same flow in Power Automate that I left open on my computer at work. It probably uses IP to determine if "another user" is working on something. I'll test this once I get back to the office. Edit: it wasn't this. I experience this even if I'm sure I only have one instance open on one IP.
If you select the second option, "save a copy of your changes", then it will create a copy of your flow. Once you open the copy, you won't have the message anymore. Unfortunately, the copy doesn't automatically get put in the same solution :(.