System.DllNotFoundException: lib/linux/x86_64/libgit2-1196807.so on Ubuntu Linux

I have difficulties with LibGit2Sharp while running Cake (with Cake.Git addin) build on Linux Ubuntu 16.04 in Docker - https://github.com/cake-contrib/Cake_Git/issues/68
But I managed to isolate issue with LibGit2Sharp only.

Reproduction steps

touch gt.cs

using LibGit2Sharp;
using System;

public class Program
{
    public static void Main()
    {
        Console.WriteLine("HI");
        var repo = new Repository("/opt/buildagent/work/e1fb3d71588668ec");
    }
}

csc gt.cs /r:LibGit2Sharp.dll

mono gt.exe

HI

Unhandled Exception:
System.TypeInitializationException: The type initializer for 'LibGit2Sharp.Core.NativeMethods' threw an exception. ---> System.DllNotFoundException: lib/linux/x86_64/libgit2-1196807.so
  at (wrapper managed-to-native) LibGit2Sharp.Core.NativeMethods.git_libgit2_init()
  at LibGit2Sharp.Core.NativeMethods+LibraryLifetimeObject..ctor () [0x00006] in <c31a5a5a3e0a424683609ecf6c55de77>:0
  at LibGit2Sharp.Core.NativeMethods..cctor () [0x00054] in <c31a5a5a3e0a424683609ecf6c55de77>:0
   --- End of inner exception stack trace ---
  at LibGit2Sharp.Core.Proxy.git_repository_open (System.String path) [0x00008] in <c31a5a5a3e0a424683609ecf6c55de77>:0
  at LibGit2Sharp.Repository..ctor (System.String path, LibGit2Sharp.RepositoryOptions options, LibGit2Sharp.Repository+RepositoryRequiredParameter requiredParameter) [0x00312] in <c31a5a5a3e0a424683609ecf6c55de77>:0
  at LibGit2Sharp.Repository..ctor (System.String path) [0x00000] in <c31a5a5a3e0a424683609ecf6c55de77>:0
  at Program.Main () [0x0000c] in <f40fe756e0ec4a4d9aed452251bd0a53>:0
[ERROR] FATAL UNHANDLED EXCEPTION: System.TypeInitializationException: The type initializer for 'LibGit2Sharp.Core.NativeMethods' threw an exception. ---> System.DllNotFoundException: lib/linux/x86_64/libgit2-1196807.so
  at (wrapper managed-to-native) LibGit2Sharp.Core.NativeMethods.git_libgit2_init()
  at LibGit2Sharp.Core.NativeMethods+LibraryLifetimeObject..ctor () [0x00006] in <c31a5a5a3e0a424683609ecf6c55de77>:0
  at LibGit2Sharp.Core.NativeMethods..cctor () [0x00054] in <c31a5a5a3e0a424683609ecf6c55de77>:0
   --- End of inner exception stack trace ---
  at LibGit2Sharp.Core.Proxy.git_repository_open (System.String path) [0x00008] in <c31a5a5a3e0a424683609ecf6c55de77>:0
  at LibGit2Sharp.Repository..ctor (System.String path, LibGit2Sharp.RepositoryOptions options, LibGit2Sharp.Repository+RepositoryRequiredParameter requiredParameter) [0x00312] in <c31a5a5a3e0a424683609ecf6c55de77>:0
  at LibGit2Sharp.Repository..ctor (System.String path) [0x00000] in <c31a5a5a3e0a424683609ecf6c55de77>:0
  at Program.Main () [0x0000c] in <f40fe756e0ec4a4d9aed452251bd0a53>:0

Mono looks up for native module in subfolder bacause of config

cat LibGit2Sharp.dll.config

<configuration>
    <dllmap os="linux" cpu="x86-64" wordsize="64" dll="git2-1196807" target="lib/linux/x86_64/libgit2-1196807.so" />
    <dllmap os="osx" cpu="x86,x86-64" dll="git2-1196807" target="lib/osx/libgit2-1196807.dylib" />
</configuration>

the file lib/linux/x86_64/libgit2-1196807.so does exist. also tried to copy it besides my .exe module.

Expected behavior

no error

Actual behavior

System.TypeInitializationException: The type initializer for 'LibGit2Sharp.Core.NativeMethods' threw an exception. ---> System.DllNotFoundException: lib/linux/x86_64/libgit2-1196807.so

Version of LibGit2Sharp (release number or SHA1)

libgit2-1196807.so

Operating system(s) tested; .NET runtime tested

# cat /etc/os-release
NAME="Ubuntu"
VERSION="16.04.3 LTS (Xenial Xerus)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 16.04.3 LTS"
VERSION_ID="16.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
VERSION_CODENAME=xenial
UBUNTU_CODENAME=xenial

# mono --version
Mono JIT compiler version 5.12.0.226 (tarball Thu May  3 09:48:32 UTC 2018)
Copyright (C) 2002-2014 Novell, Inc, Xamarin Inc and Contributors. www.mono-project.com
        TLS:           __thread
        SIGSEGV:       altstack
        Notifications: epoll
        Architecture:  amd64
        Disabled:      none
        Misc:          softdebug
        Interpreter:   yes
        LLVM:          supported, not enabled.
        GC:            sgen (concurrent by default)

LibGit2Sharp.dll.config と、スタックトレースに示されている LibGit2Sharp.Core.NativeMethods の初期化から始めます。Ubuntu 16.04 上の Mono で提供された C# プログラムを使って失敗を再現し、その後、DllNotFoundException なしで期待される動作が得られるまでネイティブライブラリの読み込みを追跡します。