I just defeated 6 withers then created a 6-beacon, then left to work on a building project (in chunks that did not have the beacons in it). I left, then returned and went back to my base (where the beacon is) and found that I wasn't getting the effects anymore. I tried moving around, then continued to look into the beacon's GUI, to find that all of them had reset and weren't powered or have any effects selected. I was confused, so powered them again, went into unloaded chunks, rejoined then returned to find the beacons were reset again. I doubt this is intentional, as it'd be really annoying to have to repower the beacons all the time, as it would be a waste of time and resources.