Show Previous/Next Tab shortcut does not work on safari

I used to have this shortcut work prior to about 2015, since then, it stop working after successive mac upgrades. I am writing now because I have new info.

The shortcut does work when opening new Safari window and creating a few fresh new but empty tabs but once you load a website into one of the empty tabs, thats when the shortcut will stop working on that tab.

I've sent feedback to Apple years ago prior to finding out this new info. Now I will resend feedback with new info, re shortcut working only on empty tabs.

Been mac user for 15 yrs.