This has been an issue in the game for a good long while, and its infuriating to have it happen to you, and also infuriating to have it happen FOR me, as I don't like winning to buggy shenanigans. The main issue seems to be that when summoned units die, it reorders turns to allow slower people to move first. This generally allows for one side to get a double turn.
If you're fighting a summoner or an engineer, and you go down and they only have one unit left, it tends to allow them to move first in the next round.
Example: Summoner Joe goes down to Axeman Bob, Carbuncle remains standing. Turn order was always Joe, Bob, Carbuncle, now its suddenly Carbuncle, Bob which allows Carbuncle to move twice in a row, winning the battle despite always acting slower before then.
In 1v1 combat this tends to always allow the summoner with auto summon to move first even with no celerity too, as turns like to be staggered.
When your wraithguard dies it can still flip-flop turn order.
50 cel ghost with a wraithguard vs a 5 celerity black knight: Ghost always moves first as expected.
Instant wraithguard dies? Suddenly the 5 celerity black knight moves first. (Starting from the next round onwards, of course.)
This is often game determinative in the least fun way possible.
Other issues:
Summoned units always act in the same section of turn order. Generally the bottom. But this becomes problematic when summoners fight each other. There's no staggering of turns for summoned units, so I've had battles where:
Person A, Person B, Person C, Person D, TEN YOUKAI OF PERSON A IN A ROW, then TEN YOUKAI OF PERSON C IN A ROW.
Which seems a bit silly for ten youkai belonging to one person to move before all ten youkai belonging to another person's.
If you're fighting a summoner or an engineer, and you go down and they only have one unit left, it tends to allow them to move first in the next round.
Example: Summoner Joe goes down to Axeman Bob, Carbuncle remains standing. Turn order was always Joe, Bob, Carbuncle, now its suddenly Carbuncle, Bob which allows Carbuncle to move twice in a row, winning the battle despite always acting slower before then.
In 1v1 combat this tends to always allow the summoner with auto summon to move first even with no celerity too, as turns like to be staggered.
When your wraithguard dies it can still flip-flop turn order.
50 cel ghost with a wraithguard vs a 5 celerity black knight: Ghost always moves first as expected.
Instant wraithguard dies? Suddenly the 5 celerity black knight moves first. (Starting from the next round onwards, of course.)
This is often game determinative in the least fun way possible.
Other issues:
Summoned units always act in the same section of turn order. Generally the bottom. But this becomes problematic when summoners fight each other. There's no staggering of turns for summoned units, so I've had battles where:
Person A, Person B, Person C, Person D, TEN YOUKAI OF PERSON A IN A ROW, then TEN YOUKAI OF PERSON C IN A ROW.
Which seems a bit silly for ten youkai belonging to one person to move before all ten youkai belonging to another person's.