Serjants are not the only unit doing Shift queues wrong. Here is an example of a bug where vills are tasked to build 4 houses, all shift queued. Before finishing the first you cancel the second house, then vill/vills (does not matter how many you choose with this bug) will build this order: 1,4,3 (2 got cancelled, so fine, but 4 should be build after 3, this can be reproduced extremely reliably… I would say as easy to repro like the “unreproducable boar bug” (List of unfixed bugs - #96 by GMEvangelos, talking about the “need more info” section)).
Just tried if this is still in the game, since the last report I have seen is several months ago. Here is the replay (bug still in game, migth be related, migth not be, but since it also is an issue with shift queue I felt this belongs here)
SP Replay v101.101.46295.0 @2021.04.07 132631.aoe2record (465.9 KB)