Hi Kaiji,
Since you are working with UI elements and that too on a browser, it could happen that the elements take time to load.
To adjust for this, we can set the WaitForReady property to Interactive/Complete. By default it will wait for a maximum of 30 seconds (this can be changed by adjusting the Timeout property just above)
To know more about WaitForReady property, please refer to this detailed explanation - Want to understand how Target.WaitForReady property exactly works - #3 by nadim.warsi
Thanks,
Nishant