Stepping code changed between versions 1.20.6 and 1.21, fixing blip-downs. For more information on blips, see https://www.mcpk.wiki/wiki/Blip.
(The code snapshots are technically from 1.19.2 and 1.21.5 because those were the decompiled versions I had on hand, but the gameplay is actually from 1.20.6 and 1.21)