I’ve never used Envira Gallery, but I suspect this is a limitation that occur with other gallery plugins when used with any tab plugin.
This issue is mentioned in the faq:
Why Doesn’t my slider or (non native WP) gallery work in any tab except the first one?
Some carousel/slider/gallery plugins render their content with zero height & width if the tab containing the content is not visible on page load.
Something that strongly suggests that this is the case can be seen if you resize your page after selecting the gallery tab. After initally being the gallery items are not visible initially, you can see that the items appear after jiggling the page width. This suggests that the gallery plugin needs to be able to detect when its content has become visible and trigger a resize in the same way it is triggered when the browser is resized.
I believe that this issue would need to be fixed in the gallery plugin rather than it being something that can easily be fixed in the tab plugin.
The thing is though when you hit refresh on the page the gallery works on the tab section
https://www.the-flag-makers.com/custommadeflags/custom-flags/
@jaseflag – I deleted one of your recent posts as you offered to pay – see:
http://codex.wordpress.org/Forum_Welcome#Offering_to_Pay
Refreshing the page is possibly causing the gallery plugin to render its content at the correct size in the same way as changing the browser width triggers it to refresh.
I can put this on my list of things to investigate. I already want to find a reliable fix for displaying google maps in tabs that are not visible on initial page load. As that is basically the same issue, the fix for this is likely to be similar.
The answer given here may help:
https://wordpress.org/support/topic/galleries-not-loading-in-tabs
It might be a starting point even though it addresses the issue when using the gallery in a different tabs plugin.
