It might be that Opera identifies that Meteor keeps an open socket, and the icon just continues to spin.
For the client they think its never completely loaded. is anyone else having this issue.
Do you have a specific version of opera? Mobile or desktop? Does this happen for both development and production?
Opera One(version: 114.0.5282.235) (arm64)
I have been regularly updating Opera, and its happened with all of them.
I have never seen it on Chrome or Safari