You need to be a Project administrator to check that...
Follow these steps
First go to Projects options in administration tab
And then select the project which you were not able to select in the board and go to project settings page (Project settings options is available at the bottom left page when you go to project), in that select Permissions option
Check the role you are in, or group you should be in the "Browse Project Permission"
Roles can be checked in the Users and Roles Option of Project settings page.
I'd more than happy to help, but the next-gen projects are built in a way that they should have only one board.
For more reference, please visit the links
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