Hyperlinks incorrectly opening a File Folder instead of worksheet tab

Simple question i hope.

I use Excel 2013 (although other users of the model use 2010).

I wanted to allow the user to navigate between various worksheets within the workbook, by clicking on the relevant links. Like a navigation panel.
All links are to worksheets within that particular workbook. I do not link to external workbooks.

To do this, I inserted 'shapes' (a text box) into my workbook using the menu ribbon.
I then right-clicked on the text box and added hyperlinks to this box.
The hyperlinks went directly to the desired worksheet and worked perfectly.

Somewhere along the way these have stopped working.
Now, when i click on the text box, instead of opening the desired worksheet, it will instead open the Folder (using file explorer) in which the Excel file is located.

When I go back to old versions of the model, the problem is not present (the hyperlinks work appropriately).
When I create an entirely new workbook, and make new buttons/links, the newly-created links work fine in the new workbook.
In the current workbook (which i need), I have tried to remove the links and recreate them, and also to copy working links from another workbook.. However, the links open the Folder (using file explorer) in which the Excel workbook is located, instead of navigating to the relevant worksheet within the workbook.

Thanks for any assistance,
Ben

Hi, is anyone available to provide advice on this issue?