To reproduce:
1) Open attached project and the scene in it on 5.3
2) Play it
3) Open 'stats' window in game window
4) Notice that the game is running at only about 30-35 FPS
5) Close it, open on 5.2
((Note: You might need to use the Conifer.spm found in Standard Assets as the project crashed for me. Simply import "Environment" from standard assets and replace the .spm files of Conifer tree. This does not change the bug outcome))
6) Play the scene
7) Notice that now it shows around 70 FPS

Reproduced in 5.3.0a4, 5.3.0b4
Not reproduced in 5.2.2p1