Verified in 5.7.1.0. I imported 5k tags and then tried to open single group. When Company tags were selected in single group it took about 20 secs to render the page. When I selected Vms & Templates and then selected different group it took about 1 secs, so tabs are loaded after they are selected.
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://rhn.redhat.com/errata/RHSA-2017-0320.html