Creating a unbreakable Continuum rift:
The easiest way is to spam shatter skills while in the Split: https://www.youtube.com/watch?v=UdTgIts-2ng
My guess of this bug would be the global shatter cooldown prevents Continuum Shift from happening.
Creating multiple rifts:
create an unbreakable rift ? die ? teleport to a waypoint within 5000(?) range ? go back to the unbreakable and do a new Split/Shift
Removing the rift:
Do a new Split/Shift. Or running 5000(?) range away from the rift will revert caster back to the rift and destroy it.