Sorry you had a crash there repeatedly! We've had a couple players mention a crash on the Level 5 beam puzzles but I haven't run into it myself. What you described with the beams can help us fix it maybe or prevent it from happening so easily. When the prisms get hit by a beam and 2 are pointing at eachother they get stuck in an endless loop where they power eachother, so I think when you added the main beam back on top of that it was crashing for you. We can probably set it to disable when two are powering eachother like that or at least turn the prism so it doesn't happen by default.
Patch 2.8 should be releasing in a few weeks and will include Level 6, so you will be able to complete the first ending then. Patch 3.0 a few months later will include more endings and more Act 2 bosses.