"Sent" folder syncing doesn't work with Thunderbird and stock mail app on MAC

But since about one week ago, I found that my email client, Thunderbird, stopped downloading new mails in "Sent" folder. Emails are sent successfully, can be seen in "sent" folder on Zoho's webpage, but no where to see in Thunderbird.

The problem is with both my iMac and Macbook running latest OS and Thunderbird.

I tried Spark, another email client, which seemed to be working fine. I also tried Apple's default mail client, which was not working either.

I tried to delete my account on Thunderbird then add it back. It didn't work.

Can anyone help me with this please?