Uneven filling is a common cause of staggered flushes. Compost depth, compaction and casing thickness must be the same from the first tray to the last.
Casing thickness is worth agreeing in writing, because DMR's manual defines casing as a 3 to 4 cm layer in one paragraph and instructs a 4 to 5 cm application a few lines later. Pick one figure for your farm and hold it.

