I can't give a strict answer to your question... What I can say is that v11.2 is based on Eclipse 2019.12 whereas v10.3 uses Eclipse Oxygen. So I do expect some differences.
Would it be possible to provide the project that exhibits the problem? Or maybe send us the workspace logs (Help => MCUXpresso IDE Save Info for Support) when using the original maximum heap size and then export diagnostics data after reproducing the problem. Is the out of memory occurring while building the project?