OnCollisionEnter2D sometimes not received, sometimes delayed

Hello,
In the latest version (5.3.1), it seems the 2D collision messages (OnCollisionEnter2D, etc...) are sometimes not received at all, and sometimes are received couple of seconds later after the collision actually occurs. The collision itself happens correctly though (objects bounce off each other). I did not observe this behaviour in any of the previous versions. Can anybody confirm this?

I'm running Ubuntu 15.10 and installed Unity from the default deb package.