Take a look at the database page for the county:
https://www.radioreference.com/apps/db/?ctid=1625
For Missoula (city) PD, the dispatch frequency (155.6100) is listed twice. One listing for analog, the other, on the same frequency, is digital. The feed provider may either not have a digital scanner, or else has the frequency programmed with a PL code (for the analog transmissions), and programmed a second time without a pl.
I would suggest that you request your thread be moved to the Montana forum. Someone there might have information of any upgrades or changes planned for this system. To do that, do
not create a new thread. Instead, click on the red outlined triangle in the upper right corner of your original post, and request that a moderator move your thread to the state forum. Someone in the area would be more likely to see it there.