Error after update

Hi there,

I just made an update from 2.8.19 version and 2.9.6, but now, when I open one of the plugins pages (login, account, register, etc.) I can’t see the forms, but only this message:

Your site doesn’t include support for the “wpum/account-page” block. You can leave this block intact or remove it entirely.

although the page is displayed normally, in any case I would like to fix the problem. Can you help me?