Hey shinichi88,
Have you attempted to duplicate the project and opening the copied version?
Also, did you upgrade from 4.7.6 during the preview build stage?
For future endeavors, whenever you upgrade a project (especially when going to an unofficial build such as the preview releases) you should create a copy of your original as a safeguard in case something happens. We do have an option in place when converting your project ‘Open a Copy’. Hopefully you used this option as it was the default.
It does seem like you have a corrupted asset or project which might need to be reverted to a previous build in order to fix.
Regards,