25 +5 Clock: reset button not working?

Hello I have a pen and am working on my 25+5: https://codepen.io/fras764/pen/yLJNJwB

My pause and start buttons work fine, but reset doesnt work as expected.

When the timer is going, and I hit reset, it simply pauses the clock, (instead of resetting it back to the number it started on), and then when i hit play again, it gives ma a NaN error.

this is not intended behaviour.

can someone please help?

Thank you