I would contact Support about this one. Sorry, I don't have any further experience to share but they should be able to help you figure out why this is occurring.
Done. I thought this was some sort of known issue as I had it similar problems several times in earlier versions already.
Tableau will skip certain data types which it cannot meaningfully support in a visualization. A common example of this is binary data, but other data types may include INTERVAL (related to date/time) and specialized date/time types such as 'datetime2' on SQL Server. Tableau added support for 'datetime2' a while ago, but it relies on having the latest SQL Server provider for OLE DB installed on your machine. This example demonstrates that other components beyond Tableau can influence whether or not Tableau can recognize and work with certain data types.
Contacting support is the best path forward here, since they can work with you to examine your application logs and gather more information about the problem. In the meantime as a workaround, try changing your Custom SQL connection to explicitly CAST those two columns to a data type you expect would be supported. A simple test would be to cast to VARCHAR(1000) or a similar string representation, just to prove that the underlying data is in fact accessible in some form. Then experiment with casting to a more specific type that you require for your analysis, such as a pure TIME type.
I hope this helps,