Unfortunately there is no easy fix for this, I tried this myself a while ago, and ended up not using any tabs for map rendering since it was the only reliable option.
I had some success with messing about with CSS but all browsers (and mobile) reacted differently.
The reason is Google maps computes it’s values on page load, there are some hacky solutions here.
https://stackoverflow.com/questions/1428178/problems-with-google-maps-api-v3-jquery-ui-tabs