Object values are lost after useState

Question

I have an object with time intervals fot every day of week.

{
mon: [['2022-05-02T22:30:00.100Z', '2022-05-03T02:00:00.309Z'], ...],
tues: [[]],
...
}

So when I'm trying to use useState

const defaultIntervals = getDaysAndIntervals({ metaData })
const [daysAndIntervals, setDaysAndIntervals] = useState(defaultIntervals)

the defaultIntervals is correct, but daysAndIntervals converting to

{
mon: [],
tues: []
}

The values of every key in this object is empty array. Could please tell me why?