I'm not sure, but the seams I'm seeing looks like the program's grid. In blender and Unity, I don't see any seams (as long as I use point filter, turn off generate mip maps, and turn off HDR in the camera settings) Most modern modelers use floating points for the UVs so without very precise wrapping it'll create seams (hence the point filter)
gltf sounds kind of obscure, but if there is a plugin for it I'll give it a shot, sure.
I'll also see about having it start in Windowed mode on startup for the future.