Rob,
It sounds like you are on the edge of what that pipe can actually do, and the speed in which you have set for the system to size at exceeds that 3.794 ever so slightly (.006). You can try speeding the water up to see if things pass that way, but if not, the system is slowing things down due to your design exceeding what is available at the POC and therefore upsizing the pipe past what you have available to use in your size list.

You are also welcome to send in your drawings and we can take a look to see if there is anything else at play here, but without seeing things, that is my best guess.

Rob,

It could be that you have a second class of mainline, or your velocity is too low.
You'd need to submit the drawing for us to know for sure.

--J

Thanks guys, I did submit the drawing via the portal.

But please add a response in this section letting all of us in the peanut gallery know what the issue/solution was. Very interesting.
Rob,
I have to imagine that you have two mainline pipes defined. One with the sizes up to 1-1/2" using PVC sch 40 and another size from 2" and above using PVC CL315. It sounds like the program is trying to slow the velocity so that one of your newly designed valves (not there before you had the problem) has a pressure requirement that requires the oversizing of the mainline. If you run a valve schedule, it may be your highest flow (but may not be).
If you have an idea which valves you have recently added, or modified, you can temporarily remove the piece of mainline that connects that (those) line(s) and resize the mainline. If you don't know which valve, I'd start from the furthest and keep trying until it works. If this is the issue, and if you have enough room on your controller, you can separate that valve into two valves.
I love puzzles. That's probably why I like irrigation design.
Hope to see you soon Rob. It's been too long.
Steve Cook