Hi Zaxtaj,
The most common causes for this issue are
using illegal characters in your project name and/or using a project thumbnail that is over 1MB in size. The latter should only happen if you manually changed the thumbnail outside the editor.
If this does not solve your problem I could have a look at your issue if you send me a zip archive of the following folders:
- Data/Public/YourProject
- Data/Mods/YourProject
- Data/Projects/YourProject
- Data/Editor/Mods/YourProject
