LumenRT - exported model location shifted

My Microstation model has been exporting fine until today. The first screenshot shows the model correctly located - I've placed trees and set up animation paths.

I've made a few changes to the buildings and terrain, but not added anything beyond the extents of the terrain. As you can see in the second screenshot, the model has shifted relative to my trees and animation paths. In OBJECT COORDINATES it shows -609.6m, 1.219km, 755.03m, which presumably means it's shifted by those x,y distances because the original location is 0m,0m,755.03m.

I'm able to manually move the model back to where my trees are by unlocking OBJECT COORDINATES, but can't seem to dial in the 0m, 0m needed to accurately and easily do so. Those numbers are greyed out.

Why did this happen? It was a common problem with earlier versions of LumenRT (remember when we were advised to place four blocks at the outer extremities?). What's the best way to diagnose this? I've tried exporting just some minimal geometry but everything is shifted by that 609, 1.219 distance.