Cannot open Unreal Engine 4 project after building

Development Getting Started & Setup
1

I built UE4.27.2 from source and tried building MS AirSim from here. After resolving all dependencies AirSim was successfully built too. But when i try to open that project i cannot because “The project could not be compiled. Would you like to open it in Null Source Code Access?”

I include the message:

Running Mono...
Fixing inconsistent case in filenames.
Setting up Mono
~/Documents/UnrealEngine-4.27/Engine ~/Documents/UnrealEngine-4.27/Engine/Binaries/Linux
Using 'git status' to determine working set for adaptive non-unity build (/home/user/Documents/UnrealEngine-4.27).
Creating makefile for BlocksEditor (no existing makefile)
WARNING: Library 'stdc++' was not resolvable to a file when used in Module 'AirSim', assuming it is a filename and will search library paths for it. This is slow and dependency checking will not work for it. Please update reference to be fully qualified alternatively use PublicSystemLibraryPaths if you do intended to use this slow path to suppress this warning.
WARNING: Library 'supc++' was not resolvable to a file when used in Module 'AirSim', assuming it is a filename and will search library paths for it. This is slow and dependency checking will not work for it. Please update reference to be fully qualified alternatively use PublicSystemLibraryPaths if you do intended to use this slow path to suppress this warning.
@progress push 5%
Creating makefile for UnrealHeaderTool (no existing makefile)
@progress push 5%
@progress pop
------- Build details --------
Using toolchain located at '/home/user/Documents/UnrealEngine-4.27/Engine/Extras/ThirdPartyNotUE/SDKs/HostLinux/Linux_x64/v19_clang-11.0.1-centos7/x86_64-unknown-linux-gnu'.
Using clang (/home/user/Documents/UnrealEngine-4.27/Engine/Extras/ThirdPartyNotUE/SDKs/HostLinux/Linux_x64/v19_clang-11.0.1-centos7/x86_64-unknown-linux-gnu/bin/clang++) version '11.0.1' (string), 11 (major), 0 (minor), 1 (patch)
Using bundled libc++ standard C++ library.
Using lld linker
Using llvm-ar : /home/user/Documents/UnrealEngine-4.27/Engine/Extras/ThirdPartyNotUE/SDKs/HostLinux/Linux_x64/v19_clang-11.0.1-centos7/x86_64-unknown-linux-gnu/bin/llvm-ar
Using fast way to relink  circularly dependent libraries (no FixDeps).------------------------------
Parsing headers for BlocksEditor
  Running UnrealHeaderTool "/home/user/Documents/Unreal Projects/AirSim/Unreal/Environments/Blocks 4.27 - 2/Blocks.uproject" "/home/user/Documents/Unreal Projects/AirSim/Unreal/Environments/Blocks 4.27 - 2/Intermediate/Build/Linux/B4D820EA/BlocksEditor/Development/BlocksEditor.uhtmanifest" -LogCmds="loginit warning, logexit warning, logdatabase error" -Unattended -WarningsAsErrors -abslog="/home/user/Documents/UnrealEngine-4.27/Engine/Programs/UnrealBuildTool/Log_UHT.txt"
LogInit: Display: Loading text-based GConfig....
Reflection code generated for BlocksEditor in 4.0051287 seconds
@progress pop
------- Build details --------
Using toolchain located at '/home/user/Documents/UnrealEngine-4.27/Engine/Extras/ThirdPartyNotUE/SDKs/HostLinux/Linux_x64/v19_clang-11.0.1-centos7/x86_64-unknown-linux-gnu'.
Using clang (/home/user/Documents/UnrealEngine-4.27/Engine/Extras/ThirdPartyNotUE/SDKs/HostLinux/Linux_x64/v19_clang-11.0.1-centos7/x86_64-unknown-linux-gnu/bin/clang++) version '11.0.1' (string), 11 (major), 0 (minor), 1 (patch)
Using bundled libc++ standard C++ library.
Using lld linker
Using llvm-ar : /home/user/Documents/UnrealEngine-4.27/Engine/Extras/ThirdPartyNotUE/SDKs/HostLinux/Linux_x64/v19_clang-11.0.1-centos7/x86_64-unknown-linux-gnu/bin/llvm-ar
Using fast way to relink  circularly dependent libraries (no FixDeps).
------------------------------
ERROR: Building would modify the following engine files:
       /home/user/Documents/UnrealEngine-4.27/Engine/Binaries/Linux/AgentInterface.dll
       /home/user/Documents/UnrealEngine-4.27/Engine/Binaries/Linux/Android/libUE4Editor-AndroidDeviceDetection.so
       /home/user/Documents/UnrealEngine-4.27/Engine/Binaries/Linux/Android/libUE4Editor-AndroidPlatformEditor.so // and there goes a list of UE libraries.

Also I noticed that by some reasons i cannot open C++ projects in UE4Editor (only blueprint ones). When i try to do it Unreal gives me the same error (that it would modify engine files).

Additionally:
I just opened .uproject file and noticed that the field “EngineAssociation” contains this instead of engine version number. Why?

{
	"FileVersion": 3,
	"EngineAssociation": "{6D2C4ABF-5245-4F2E-B020-E61D77E8F0D5}",
	"Category": "",
	"Description": ""
}
2

About this small addition: That’s how your source-builded and installed-builds are named by default - with random guid. Only launcher’s engines are named 4.27, 5.0, etc.
Iirc that’s called BuildId and can be set manually to any constant string before build if you need this by some reason. But unless you have a special reason to set engine’s BuildId manually, you absolutely fine with generated id

3

Also noticed another thing:

I tried to compile the project with GenerateProjectfiles.sh script and makefiel in UnrealEngine source code directory.
But when i try to open it, UE tells me that the project was built in another version of UE. So i decided to put right version manually, but the error keeps appearing.

But then i decided to do following:

In my .uproject file:

{
	"FileVersion": 3,
	"EngineAssociation": "{6D2C4ABF-5245-4F2E-B020-E61D77E8F0D5}",
	"Category": "",
	"Description": "",
	"Modules": [
		{
			"Name": "MyProject3",
			"Type": "Runtime",
			"LoadingPhase": "Default"
		}
	]
}

if i delete lines:

"Modules": [
		{
			"Name": "MyProject3",
			"Type": "Runtime",
			"LoadingPhase": "Default"
		}
	]

The project starts. Why is that? What are these lines for?