Description:  Was playing a multiplayer game with my boyfriend. Noticed some lagging in the last round (about turn 100) and a few rounds later my boyfriend got kicked out of the game between rounds. 
I finished the round and tried to go back to the main menu, then the game crashed and I got the notification to send the folder (see attachement) to the developers. 

Steps to Reproduce:  Not sure if that is reproducable, first time we had this. 
Version:  1.5.28

Notes: If there is any information I can provide you with to get a better image of the situation, ask away :)

Ah yes:

System.TypeInitializationException: An exception was thrown by the type initializer for Mono.CSharp.CSharpCodeCompiler ---> System.IO.FileNotFoundException: Windows mono path not found: D:\Spiele Steam\steamapps\mono\mono\mini\mono.exe  at Mono.CSharp.CSharpCodeCompiler..cctor () [0x00000] in <filename unknown>:0

..again.

This error has come up a lot lately. It's caused by Unity, the engine that the game runs on.

You can read one thread about it here. In that case he fixed it by changing the galaxy density.

Updating to the latest version of Windows 10 has fixed it.

You can also try set "-force-opengl" in the Steam launch options. To do so, right click the game in Steam, go to properies, then click on "Set Launch Options...". That has fixed it.

If you are missing Mono you can also try installing it then copying the Mono folder to steamapps. You can find the installer for Mono here. I haven't actually seen this fix, or any below work yet. The real problem is not that you are missing Mono, it looks for something in Microsoft .NET and when it can't find that it resorts to looking for Mono.

This could be caused by not having Microsoft .NET Framework 4.5.2. You can download it here.

You can also try installing C++ Redistributables (vcredist). It can be found here: x86 (32 bit OS) x64 (64 bit OS)

You can also try going to the "C:/Program Files (x86)/Steam/steamapps/common/Endless Space 2/EndlessSpace2_Data/" Folder and deleting the mono folder then verify the games files with steam. It should redownload the folder correctly.

The devs have commented there is a known issue with Unity and non-English characters, they said: Some people using non-english OS and international characters in their steam path could not launch the game. Such characters are badly handled by the low level layer of Unity, Mono. We have performed a workaround in the code, (better than having to reinstall Steam to a path without accents)  waiting for a cleaner solution from Unity.
I have seen others propose a fix to this that involves deleting fonts which are corrupted. Is he using a non-English computer?

Well thanks for your really big reply :) 
Game starts fine right now, we can even load in together with no problem (that was a problem before the latest patch). 
So don't know if I need to fix anything. 
Game just gets laggy as hell, so we quit it for now, but that's probably another bug introduced with the latest patch :/