I'm not sure if this is only on realms, or just any world, but I've noticed many of the command blocks I've placed not working. I will input a command and they'll usually work for a while, but then they'll just suddenly stop working for no apparent reason. I know it's not a problem with the format of the command, because 1) the commands were working before, and 2) all I have to do to fix the issue is copy the command block with the NBT and then break it and replace it. It's a quick fix, but it's still annoying because of how many command blocks I have in my worlds, and they also keep not working over and over again so I have to replace them very often. This isn't new in 1.14, but I waited to report the issue because I was hoping they already were planning to fix the problem when it was released.

This issue also appears to only be with command blocks that are always active and repeating, because I guess command blocks that need redstone get a block update right before it activates the command; or it could be they only have one job, instead of working constantly and checking for if the parameters are met. I'm not sure if there isn't an issue with regular redstone needing command blocks, but I haven't noticed anything.