Thanks, Rui.
I replaced the tabs.php file.
The problem was still there.
I re-saved all the tab titles through the page builder.
The problem was still there.
I switched to the classic editor, and the tab ids are actually correct in the code. As soon as I view the live page, though, and hover over a tab, I can see that it’s picking up the wrong link (hover shows #213 instead of #week1, and link does not work).
If you won’t get chance to fix this for a while, is the best plan to go back to an old version of the theme (3.3.32 seems to work) until you can fix this? Will that cause any other issues since I’ve now upgraded WP to the latest 4.7.4?