It seems like there is a problem with the VR Experience Helper of the new Babylon version.
After entering and exiting VR, the mouse controls for the non-vr camera are not working any more.
Keyboard control is still working.
This can be reproduced with the Default Sponza Playground https://www.babylonjs-playground.com/#JA1ND3#6
If you switch the Playground to the the Stable Version 3.3.0, everything works as expected.
I am using Win 10, Firefox 66.0.3 64bit and Oculus Rift.
I tested BabylonJS 4.0.0-alpha.32 and 4.0.0-beta.6. Both showed this problem.