Eclipse can not resolve dependency in eclipse, unless the dependent project is closed

I’m upgrading an old Eclipse setup and ran into a strange issue with m2e workspace resolution.

I moved from Eclipse 2021 to Eclipse 2025.
I created a completely clean Eclipse installation and workspace, imported all my projects, and installed all required plugins.

However, I now have this problem:

Project A has a Maven dependency on Project B (declared in A's pom.xml)

If Project B is open in the workspace, then Project A cannot resolve imports or references to Project B

If Project B is closed, then Project A compiles fine (but now under Maven Dependencies the jar of Project B is present, not the project folder)

If I disable "Resolve dependencies from workspace projects" in Project A it also works, but this slows down development, as I have to build Project B after each change for Project A to pick up the changes.

So workspace resolution itself seems broken.