Thanks for your advice.
Actually, I did disable all plugins one by one and checked. But, nothing changed. So I decide to rebuild WordPress site. I hope this would resolve the issue. And, right now, I’m not sure if I use PM Pro after rebuilding it. So if I use PM Pro, I will let you know the result.
Hello @andrewza
Thank you for your prompt response. I did WP_DEBUG and found no error.
And I tried to add new membership level, but couldn’t. Also, when I tried to edit some data of one of members, for example, “Invalid user ID” was shown up on the screen.
Please advise me.
Thanks in advance.