do you have the add invoice/ticket/client etc button or is that missing?
i got the similar issue after update where blank page with no add data button or list of existing data tables, but only sidenav and topbar menu.
In my case, swapped the php versions (if you run multiple) and where older php version failed to load all the functions of the current page, the newer version of php helped. Changing from FastCGI to FPM can help as well, but tail the php error logs if you have access, cause then you can better trace the issue.
assuming you run it on a VPS with full control and you can manage it.