If there are any DLLs other than those for Rimworld, such as 0Harmony.dll, in the following folder, the Prestarter will output an error when starting Rimworld and Rimworld will not start.
Steam\steamapps\common\RimWorld\RimWorldWin64_Data\Managed
The error log is here
http://seeki.sakura.ne.jp/Player.log
The mod list is here
http://seeki.sakura.ne.jp/ModsConfig.xml
Normally, such DLLs would not be placed in the Managed folder. However, I am a mod creator and placed the DLL there for a special reason.
This problem only occurs under special conditions and is not relevant to most people.