Selecting a sheet from multiple open sheets requires two clicks. Why?

If multiple sheets are automatically opened when starting Excel, accessing one of those sheets requires two clicks. Why? I have 12 worksheets that open when Excel is opened. Hovering the mouse over the Excel icon on the taskbar displays all of the open sheets. Previously, I could simply move the mouse to the desired sheet, click, and it would open. Now, if I do so, it doesn't open and I need to repeat the operation, which always works the second time. If I hover the mouse over the desired worksheet and the name appears in bold type, it will open on the first attempt. This problem started with the last Office 365 update. Can it be reversed? Thanks in advance for any assistance!