Hi. I can not see in bank section unlinked items today which they were there yesterday. What happened to them? How can I figure that out?

Hi alper-safiyaa-co, thanks for joining the Community.

You can view the audit log of your QuickBooks (Cog > Audit log) to check if these transactions were reviewed by another user with access. 

Transactions that have been reviewed  (added or matched) from the 'for review' bank tab will then appear under the 'categorised' bank tab, where you can select Undo in the action column to move back if they were added incorrectly.