For some reason the calendar isn't rendering correctly and the only recent change we have made is upgrade to react
<DatePicker
label="Rent Begin"
placeholderText="Pick rent begin date"
minDate={moment()} // Today is minimum date
weekStart='0' // start on sunday
selected={this.state.rentBeginMoment ? moment(this.state.rentBeginMoment) : null}
onChange={this.handleChangeRentStartDate.bind(this)} />

I am getting the same
I guess u people are forget to import the css file
i.e.., import 'react-datepicker/dist/react-datepicker.css';
Importing the CSS file working for me. Thanks @Yamini-Govardhani
It still didn't work for me
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Most helpful comment
I guess u people are forget to import the css file
i.e.., import 'react-datepicker/dist/react-datepicker.css';