You don't get guarantees with living animals and their behaviors. Anything can possibly happen. You will need to monitor the situation.
The way I understand this they are all the same age and have been raised together. This is a recent occurrence. If I'm wrong please correct me.
I think different things could be going on. It could easily be the difference in maturity and will sort itself out as the ones getting beat up mature. As they reach maturity at different times it is fairly normal for the pecking order to get rearranged. With mine this is usually not that noticeable but each chicken has its own personality. Sometimes it does spark behavioral problems.
I find that how much room they have can have an impact on behaviors. I don't know how much room they have or if there are certain times this happens. This could be good information. Is it in the coop, in the run, or on the roosts? They get bigger as they grow. Have they grown enough that what used to be enough room is now tight. You don't say where you are, again it could be good info. Has a change in weather caused them to be restricted to certain areas? Are you managing them any differently, maybe due to a change in weather or the change in daylight savings time?