When you talk about users not having the issues when they are not connected to a Meraki network. Do you mean different switches/AP's in the same office space or do you mean you have a branch without Meraki gear and a branch with?
Also are the Zoom calls between your office and an external site/external partner or internal to a site?
In case of different sites what is the scale of the current site (amount of unique endpoints, intervlan (east-west bound) routing volume, local/internet (north-sound bound) volume and what MX model are you using?