I have a problem with my gmail, for about two days my emails are not syncing. Using eM client 7.2.34959.0 on Win 10 64Bit.
Assuming you are using IMAP/SMTP for Gmail and all your mails are on the Gmail server, the easiest solution is to remove the account and then add it again. But you should not use the _ automatic setup _. Instead, click on Mail , then choose Gmail and follow the instructions.
Of course you could also check all your settings and try _ Diagnostics _, but in my experience, just removing the offending account and adding it again is the simplest solution.