Simplest use case - the default value is a string that exactly matches one of the manually entered Options (the default is "Option 2" and that's what the select shows)
Dynamic simple option - I have a simple JSON array and I use JS to pull a string (the 0 index value in the array is "Option 3" and that is what the Select shows - I put the options out of order just to try to show it is dynamic)
Dynamic mapped option - my options are now mapped to another JSON, but still works just fine (the 0th value is "Option 3" which gets selected (note: not "option 3" with lower case):
Dynamic mapped option with labels - you can set value and labels to be different arrays with an object used as a data source for your drop down. It still seems to work fine (the value at index 1 in my array is 4, which maps to index 3 of my mapping values, and index 3 of my label values is "monkey" which is what is shown):
Does one of these help with your situation?