Wireless keyboard suddenly skipping (not responding) to some letters and numbers

Like which ones exactly? You need to tell us that...

If by chance it is 789uiojklm, see

Fix for 789uiojkl keys or numeric keypad … - Apple Community

If something else, be specific and someone can probably help

How is the power or charge level in the board? There are models with self-contained rechargeable batteries and other that use replaceable AA batteries. That is why we need to know what you have to effectively help.

Click the Bluetooth icon in your menubar to see the power/charge level:

or do System Settings > Bluetooth