We’re working on an update to solve these recent issues with Zeplin not connecting. Please stay tuned, and sorry for the inconvenience 
EDIT: forgot to say, sorry: since this issue is happening only with the latest version we released this week (2025.1.1), the workaround for now is to download the previous Sketch 2025.1 from here.
See this topic as reference: Zeplin not working with 2025.1.1