UnityTimeOutException: The Unity environment took too long to respond.

I am using obstacle tower 1.2 binary and mlagents-envs-0.6.2, under a Linux environment.

In [1]: from obstacle_tower_env import ObstacleTowerEnv

In [2]: ObstacleTowerEnv.ALLOWED_VERSIONS
Out[2]: ['1', '1.1', '1.2']

In [3]: env = ObstacleTowerEnv('./ObstacleTower/obstacletower.x86_64', retro=False, realtime_mode=False)
Found path: ./ObstacleTower/obstacletower.x86_64
Mono path[0] = './ObstacleTower/obstacletower_Data/Managed'
Mono config path = './ObstacleTower/obstacletower_Data/MonoBleedingEdge/etc'
Preloaded 'ScreenSelector.so'
Preloaded 'libgrpc_csharp_ext.x64.so'
Logging to $HOME/.config/unity3d/Unity Technologies/ObstacleTower/Player.log

I get the following error:

UnityTimeOutException: The Unity environment took too long to respond. Make sure that :
         The environment does not need user interaction to launch
         The Academy and the External Brain(s) are attached to objects in the Scene
         The environment and the Python interface have compatible versions.

I am correctly using the obstacletower 1.2 binary, and it was a head-less mode.

2f6c7ca247c98cdb27776bfde28037a36d1280a4  obstacletower.x86_64

Related Issue?

I checked #44 #46 but they were about Windows or before 1.2 release. I had tried out v1.0 long time ago, and I remember there was no problem at that time.

Executing the binary from the console (with strace) -- nothing follows after some system calls.

... (many lines) ...

munmap(0x7f6f1ac54000, 92100)           = 0
munmap(0x7f6ee85f5000, 2109768)         = 0
munmap(0x7f6ee83ef000, 2118024)         = 0
open("./ObstacleTower/obstacletower_Data/Resources/UnityPlayer.png", O_RDONLY) = 4
fstat(4, {st_mode=S_IFREG|0644, st_size=24711, ...}) = 0
brk(0x415c000)                          = 0x415c000
read(4, "\211PNG\r\n\32\n\0\0\0\rIHDR\0\0\0\200\0\0\0\200\10\2\0\0\0L\\\366"..., 1048576) = 24711

What should I check for this issue?