I'm late to this thread, did you get the firmware to update?
I had an issue when I tried to update using my ISP. My computer is connected to my WiFi and through that to the ISP. Either the WiFi or the ISP is blocking Sentinel from connecting to the Uniden server. I connected my computer via my Verizon jetpack bypassing both the router and the ISP server.
I'm not an expert, but my guess is that my ISP (Spectrum) is blocking the port that I needed to connect to the Uniden server. Going through Verizon via my Jetpack worked with no issue. As I recall I had to do the same thing with the last update as well.
Just tried 1 second ago would not up date not working for me !