18% isn't bad but the extras might be diluting down the protein. Occasional treats are fine and they do give the birds something to peck at, but try to keep it minimal.
Unfortunately even birds that have been raised together and lived together for years can be affected by pecking order changes and what was once plenty for them to live peacefully becomes no longer enough. With spring in full swing, hormone changes might be what kicked off this bad behavior, or it could be a hold over from being more tightly confined in winter, I don't know.
With your set up, one issue is that while you technically have enough space for 10 in terms of footprint, the reality is you have 1 narrow run that's too small for the number of birds, then a 2nd narrow run - and the narrowness means it's difficult to add clutter and items to keep the birds occupied and to provide hiding space for a bird that may be getting chased around by another. The 3rd run space is bigger but sounds like mostly a summer thing, which is fine for that time of year but doesn't help with crowding or boredom during winter.
You can try the pinless peepers. It might turn out to just be the one problem bird, or you may find that there's others contributing. Peepers aren't a long term solution but sometimes the goal is just to break the habit and hope for the best.
If that doesn't work, you're looking at having to rethink the set up - maybe that 3rd run can be roofed over to be put in use permanently, for example - or the possibility of rehoming the problem bird(s).