The best solution in case nothing helps could be microsoft project recovery tool
Visit microsoft article on - [https://support.microsoft.com/en-us/help/323330/how-to-back-up--schedule--and-restore-a-microsoft-project-server-datab|https://support.microsoft.com/en-us/help/323330/how-to-back-up--schedule--and-restore-a-microsoft-project-server-datab]
This is the resource of manual: [http://project.mvps.org/faqs.htm#Handling_project_file_corruption_and/or_bloat|http://project.mvps.org/faqs.htm#Handling_project_file_corruption_and/or_bloat]
Or alternative variant can be [https://onlinefile.repair/en/project.html|https://onlinefile.repair/en/project.html]