I’ve ever met this case, with my website: https://standavietnam.net/
That is when my banner is taken from other websites, which do not have SSL / HTTPS installed. After changing the banner, the address bar changes to green.
You try it!
(Sorry for my English not really good)
If by “green address bar” you mean an Extended Validation (EV) certificate.
LE doesn’t provide EV certs only Domain Validation (DV) certificates; which will not show as green.
If you have problems that other people don’t have, you might have some kind of browser extension in your web browser that is modifying the content of the page and adding tracking elements to it, which the browser recognizes as insecure because they come from a non-HTTPS origin. This could be malicious software that you installed by accident or without realizing its malicious consequences. There is a very large amount of malicious software like this out there in the form of browser toolbars and bad browser add-ons.
Another unusual possibility would be that something about the site itself generates different content depending on where the user is connecting from, so if the site shows slightly different content to people inside Vietnam and outside Vietnam, maybe nobody outside Vietnam can confirm the nature of the problem. However, this explanation seems quite unlikely to me.