Thunderbird on MAC not downloading "sent" folder

From a few days back, Thunderbird on both of my MACs stopped synchronizing "sent" folder of my account. Emails went through, you can see them in "sent" folder logging into zoho webpage but not in Thunderbird.

I did a bit test and found that gmail sent folder works fine on Thunderbird, sent folder works all good on a few other clients (spark etc) just not Thunderbird.

Please shed some light on this.

Thanks.