The problem was triggered by having a set of compressed iron blocks (part of a refinery) on the chunk border. According to TickProfiler, those blocks -- and only those blocks -- used up to ten milliseconds per tick, each.
As you can see on http://i.imgur.com/Im5x9Qb.png, it escalates over time. The dip at the end happened when I broke the blocks on one side of the border. The sudden spike before that was when I teleported to them; it seems that chunkloading doesn't resolve this problem.
The problem was triggered by having a set of compressed iron blocks (part of a refinery) on the chunk border. According to TickProfiler, those blocks -- and only those blocks -- used up to ten milliseconds per tick, each.
As you can see on http://i.imgur.com/Im5x9Qb.png, it escalates over time. The dip at the end happened when I broke the blocks on one side of the border. The sudden spike before that was when I teleported to them; it seems that chunkloading doesn't resolve this problem.