I have had a Christmas Cactus for 3 years now and for the first time the leaves are breaking off at the ends of the branch (or stem). Is it a light or water issue or what?

If you have never pruned your holiday cactus, it may be pruning itself. It also could be a light or root problem.

Your plant should be close to a moderately sunny window - north or east windowsills are best. If you have it more than several feet from the nearest window or off to the side of the window, it may not be getting adequate light.

If you repotted recently, that may have damaged the roots. If you are not letting the the soil dry out quite a bit between waterings, then root rot may have set in. On the other hand, if you are allowing the soil to get too dry, that can cause leaf drop.

Why now, you may ask. That is because if light and/or watering are off just a bit it may take a long time before the symptoms show up.

This particular cactus is very temperamental when it comes to moving it. If you changed the position of this cactus, that is reason enough to drop leaves.

While it is true that holiday Cactus flower buds are sensitive to any movement relative the light source, such moves should not cause leaf drop.