Powering several command blocks at the same time gives inconsistent run order

Verification builds: Release 891562
Summary: When powering multiple command blocks during the same tick, the order in which they run seems arbitrary and has been observed to change after a relog.

Impact: Breaks the primary mechanic of Jurassic Depths and causes a certain puzzle to be unsolvable.

Repro Steps:

1. Build the shown contraption.
2. The bottom command block should contain /fill ~ ~1 ~ ~ ~5 ~ redstone_block
3. All other command blocks should contain /say commands in ascending or descending order.
4. Power the bottom command block

Observed Results: Text is printed in some arbitrary order. Adding an additional command not only adds it in an arbitrary position, it also shuffles the order of the existing blocks. Relogging has been seen to change the order as well after subsequent powerings.

Expected Results: The commands and their chains run in an order guaranteed by some objective criteria.

Screenshots/Videos attached: Of the contraption.