When copying data from somewhere and pasting, always use Paste Special as Values.

Excel - Paste Special as Values
Excel – Paste Special as Values


When you right click inside the table (wherever you want to paste data), you may see this option under the Paste Options as shown above as Option 1. If not, then click on Paste Special and choose paste as values under Paste Values sub-menu (shown as Option 2).

Default Pasting method (Ctrl+V) will paste not only the values, but any formulas and formatting. This is not desired as 1) it may create links to external files and 2) it will overwrite the formulas and formatting expected in the template. Please avoid.