I did easy way to fix incorrect map size when you display map on tab, for example on not active tab.
Here example. You create tabs, and publish map on the second tab
when you click on second tab to show map, you’ll get wrong map
You can see not all tiles, and it doesn’t refresh correctly when you draggin map.
Now how fix it.
Create Map Override.
On Map tab enter container selector in jQuery notation, where map div is located, ie tab div which displayed/hidden when you click on tabs.
Assign this override to map, go to map details, in advanced options there is a list of available overrides.
And you’ll see you map like