Issue with thunderbird

Folks, I've been using thunderbird as my email client for a long time and I've seldom had any issues with it, but now I'm having a strange problem and I'm not sure where to go for help. The issue is I use thunderbird as my email client for 3 email accounts. Thunderbird downloads my email for 2 of those accounts, for the third, which happens to be gmail, it tells me there are no new messages to download. The last email thunderbird downloaded for my gmail account is May 4. If I look at my gmail account using chrome it shows emails up to May 15. Also I receive my gmail email on my Samsung S7 smartphone and it shows all recent email up to May 15, so I don't think the issue is with gmail. Does anybody know what might cause this behavior and how to fix it? Gmail is my primary email, so I really do need to get this fixed. Any help is appreciated. Thanks, Paolo