I have searched about this bug and i found it similar to this https://bugs.mojang.com/browse/MCPE-13983
It's almost the same bug except this only happens in Realms. It happens occasionally but since I have a redstone contraption that uses a lot of 4-tick repeaters (ex: LED glowstone lamp lights), it's a pretty bad bug. It does fix it self sometimes but then a few minutes later, the redstone repeaters work like 1-tick repeaters again. Note that this is on Realms and not on normal worlds. There is a way that I fix it (I just go ahead and destroy and replace the repeaters and set them to 4 ticks) but if I have to do that for every other moment, I'd rather not play. I hope this gets fixed 🙂
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0.15.9, not fixed yet, mechanisms accidentally gets broken after trying to play with my friends on realm
Represented on .15.6 MCPE Realms, usually after somebody joins your server, or reloged few times