#tab-2 appearing on URL

For some reason when some of my customers click on product pages #tab-2 is appearing on the URL.

This is causing problems with the toggles – they will not open and instead the customer is directed back to the top of the page.

This is only an issue for some customers using various internet browsers on only some product pages. Does anyone have any idea why this is just appearing?

I have tried telling them to simply delete the #tab-2 and it should work fine but they are still experiencing problems.

All themes and plugins are up to date.