Affects Version/s: 1.14.60 Hotfix
Fix Version/s: None
OK so this will be a bit of a long one to explain, sorry. if you have a repeating command block with a somewhat large delay (say 100), it is pretty easy to make it run on multiple cycles (not the correct term but whatever).
if you were to power a repeating command block (with needs red-stone of course), and set it for a delay of 100 ticks, then unpower, and repower the command block while its still waiting its delay, it will start another loop of 100 ticks of the cycle, while the first 100 tick delay is sill active. once the original delay runs out, it will still execute it's command, and trigger any chain command blocks attached to it. and it wouldn't just end there either, it will keep going, starting another 100 tick delay. the second loop is also fully functional, and it is like you have 2 command blocks on 100 delay in the same block. this is not limited to 2 loops, however, and you can have as many as you want, it seems. the only way to stop it is if you unpower it, then let the loops finish their delay, then they realize they aren't powered and will stop.
this really isn't too hard to replicate, as all it takes is some unpowering and repowering of a repeating command block, with a command in it such as "/say hi", and the issue should become apparent.
if you want to see it in more detail, you can use these commands that i used to find out the issue.
/scoreboard objectives add timer dummy timer
/scoreboard objectives setdisplay sidebar timer
/scoreboard players set time timer 0
/scoreboard players set lastlog timer 0
/scoreboard players set delay timer 0
there should be a scoreboard on the right of your screen with 3 values
now we will have to use a few command blocks to help us out. first is an independent repeating command block on always active and no delay, with the command: "/scoreboard players add time timer 1"
the time on the left of the screen should start to quickly go up
now we can leave that one alone, and move on to a chain of 3 command blocks. the first is a repeating command block with a delay of 100, and set to needs redstone. this one should have the command "/scoreboard players operation delay timer = time timer"
the second one is a chain command block, with no delay, on always active, and chained from the repeating command block. this one should have the command: "/scoreboard players operation delay timer -= lastlog timer"
the last command block should be identical to our second command block in this chain, aside from being chained from the second command block, and the command being: "/scoreboard players operation lastlog timer = time timer"
now that should be all the commands we need. first, place a redstone block next to the repeating command block that is part of the chain of 3 command blocks. the delay may do something weird for a little bit, but after about 10-15 seconds, it should stay at 100. this means it works, and that the repeatoing command block is, in fact, going at a delay of 100.
now to see the bug, quickly break and replace the redstone block a few times, and when you are done breaking and replacing the redstone block, make sure that you left the redstone block there the last time so that it is still powering the repeating command block. now watch the delay go a bit odd, as the repeating command block isn't waiting 100 ticks each time, but less as it is running multiple waiting cycles and activating a command every time. eventually the delay will keep repeating the same numbers over and over again, as each loop is consistent, and repeating.
that is all. hanks for listening, and hopefully for fixing this one day. i also hope this isn't a repeat, but as far as i can tell, its new. thanks again!
edit for clarification: when doing the long demonstration, watch the delay. that is the delay between each time the command block activates. in the beginning, it is 100, what we set the command block to. but after we spam the redstone block, it starts to jump around because it is being triggered on loops that shouldn't be there, making it trigger much earlier than it should.