I think what @hernantorrisi is experiencing is due to the new Google Chrome SameSite cookie policy (which is still rolling out to some users). Due to SameSite, he says you cannot launch a Zoom session from within an iframe even AFTER logging in. It impacts users that have already had SameSite enabled in their browser, but that seems to be a large percentage of Chrome users.
Based on your answer in this thread (Web SDK Can't Join as Host) the only way for a host to launch a Zoom session from within their browser via a third-party application is to use an iframe. However, due to Chrome SameSite, the iframe solution is broken for many many Chrome users. You can validate the error by forcing your Chrome SameSite flags to enabled and testing with the codepen posted above.