Thank you for reaching us out.
Probably the list with items which the drop down contains appears dynamically in the DOM tree when the drop down is toggled. To update the current state of the DOM during execution you will need to refresh it. Please try inserting the following line of code between the toggle action and the one which selects the item from drop down:
Alternatively, if the SelectByText is still not working, you could try to locate the element to select in the DOM tree - it will probably be a ListItem with certain text content - and directly click on it.
In case you will need further assistance, please share the DOM tree of the page with drop down at the moment when that is opened to select an item.
Thanks in advance!