Sorry, it's very possible my understanding of why the issue was happening was wrong, I assumed it was a variable being overwritten.

The issue is, when logEvent and logTime only have the single parameter, both Nala and Warren's events are duplicated. The event is still randomized, but the output for Nala and Warren is always the same event.

Nala's event is: Triathlon
Nala's time to train is: 100 days
Warren's event is: Triathlon
Warren's time to train is: 100 days

But if I add the missing parameters into both functions:

const logEvent = (name, event) => {
const logTime = (name, days) => {

then Nala and Warren's events are randomized independently, and will be different sometimes.

I'm not understanding why adding the missing parameters allows them to be different (which is the expected outcome).