Doesn't sync all of my emails, just random ones

I just started using eM Client today. I set up my Gmail account and it successfully accesses it and displays some of my emails - but only some of them. New emails that arrive after installing eM are all there, but of the thousands of emails that are older than today it looks like it has just chosen random ones to sync and others to not sync. I don’t see any pattern or criteria to determine why it chose those and not others. This is true for both the main Inbox folder as well as all of the other folders.

My Gmail account is set up for IMAP.
The account works correctly with other clients such as Opera Mail on my desktop, as well as the default Mail app on my Android phone.

I am using version 7.1.33042.0 on Windows 7 64-bit. There are no errors in the log tab.

Does anyone know what is going on, and how to fix this?

It may be that eM Client did not complete the download of messages. You can right-click on the folder and choose Properties > Repair. See if that makes any difference.