Storyline 3: Enable Next Button Triggers No Longer Working Correctly?

Hello. 

So, for our courses, we would disable the next button until the user has completed some type of activity on the page. Typically the triggers we use would either be: 

• When timeline starts on a slide layer, or
• When all relevant buttons are visited.

We have done this for a few years with no problems.

However, very recently, we have encountered an issue where sometimes, after all these things are done, the next button would still not be enabled. It would work for me but not someone else etc.

But if we clicked the previous button and then return to that slide, the next button would show up as enabled. Nothing has changed with how we have created these triggers. Does anyone know why this is happening? We are using Storyline 3.