world,
I have been playing with Blender 2.8.1 for a couple of months and recently keep running into the same issue with a mirror modifier.
When I apply the modifier the mirrored object is way off-centre, like this:
I am able to solve the issue by simply joining the asset I want to mirror and another asset which already has a mirror modifier attached, however this adds the material from the latter object to the object I'm trying to mirror which is undesirable.
Any techniques to help me create a perfect mirror when I'm working with multiple assets will be much appreciated if provided.