I was using mine up by Marcell today (I bet you know where that's at) and I was able to replicate your problem I think. I was in some young aspen stands (leaves all off of course) where there's a lot of multipath potential, but not a lot of blocked sky. I was running off a WiFi hotspot from the MNDOT VRS.
I started work with the default 6 engine / 4 constellation settings. It worked ok when I was using the precise topo preset, because that only requires 1 engine. When I went to shoot a boundary monument (using boundary preset) it would never initialize more than 1 engine no matter how long I waited, so I was dead in the water with that setting.
Without moving the rod, I switched to the 6 engine / 2 constellation setting (GPS + GLO only) and after resetting, it immediately had all 6 engines fixed and started "making popcorn" - that's what I like to call the epochs sound. So I don't think sky visibility was a factor.
I switched back and forth a few times to see what happens, and it had no problem when using GPS + GLO, but it seems when Beidou is in the mix, it can't get a lock. It was a little better when I used the 6 / 4 settings later this afternoon, so I don't know what's going on exactly, other than to say I think I'm having the same problem. I'm pretty sure the GPS + GLO + GAL can play nice together, so maybe there's a way to exclude all the Beidou satellites?