Outlook and owa search brings irrelevant results

Hi,

We have exchange server 2016 15.1 ‎(Build 2375.7)‎. single server. no DAG.

When I search for word ie "karsan" in outlook instant search, it brings all results starting with "kar"

Owa search results is the same. Only Outlook advanced find brings correct results. Archive searches are fine. only exchange mailboxes are affected.

What i tried

• recreated index on clients
• deleted guid.single on server
• moved a mailbox to another database and disabled indexing

Issue happens on all clients and owa.

Do you have any suggestions?

Thank you