There are several ways to "reset" the pointer, but it can glitch out again at any point. Its not stable for any reasonable amount of time. IE it can happen in 2 seconds even after reset. Agreed its very difficult to do any precision work, heck its even hard to resize a window with the cursor issue.
Unfortunately as we know, Apple doesn't seem to give too much considerations to the professional users and artists. If it was in IOS it would be fixed tomorrow.
The fact that it occurs at the barrier of the MST screens, and the fact that the mouse cursor blends right at the junction seems like it COULD be a driver issue. Is everyone running a Nvida GFX card with this issue or has somone experienced this issue with like Intel Native graphics too? Though...... its sierra only and not in el capitan so... still seems like Apple's fault.