Okay, this is flat out weird.
I am unable to get a valid connection when entering any Coast Starlight point to any Empire Builder point, including major ones, like EMY to MSP. I was able to get the 14-28 connection to Michigan points like ROY or DET. Checking for other eastern trains, I checked CLE and BUF on the LSL and was unable to get a 14-28 connection. I used the same departure date for all attempts. I think that pretty much excludes track work. This is reservations system issue, whether a mistake or deliberate.
The connections have to be entered manually into Arrow city pair by city pair, not even train to train. Normally, in checking guaranteed connections from smaller cities, if the connection doesn't show, check the major cities on those routes. If those show, you have a guaranteed connection. Like Dunsmuir-Elko may not show an 11-6 connection, but Portland-Salt Lake City does, so 11-6 is a guaranteed connection even if you have to force it through Multi-City. This is not the case for any Coast Starlight points and any Empire Builder points no matter how major. So far that connection only shows when booking to Michigan.
It may be a system artifact, like a recent issue where any reservation from New York to Seattle or Portland would put you on a bus at Spokane, but booking Chicago to Seattle or Portland was just fine.
I find the total lack of 14-28 connections on those trains' own points disturbing. I would suspect that cutting that guarantee is a possibility, and as they remove city pairs they either forgot or haven't gotten around to Michigan points. However, as error prone as Amtrak is, it also could also just be a screw up, and that connection will reappear in a few weeks.
Just an FYI, if they are in the process of cutting it, but they issued a ticket with it, they'll honor the guarantee.