It happens for me both on the browser client and the Linux AppImage.

Problem:

When composing a new mail, I used to be able to type the receivers name in the address field and get hints for the correct e-mail address / contact. Since recently, I don't get anything anymore. Same for when searching for mails byu the contacts. In the search field, there is no hinting anymore and search works considerably worse because of that. I have contacts in the contact Tab and I even exported, modified and re-imported them.

I can open the contacts when pressing "to:" but it shows only 2 contacts. However it reflects the changes I made to the contact groups before re-importing.

I tried deleting "Zoho Desktop" in my .config folder, but to no avail.