One thing to point out is that the origin of the error goes back to between round 4 and 5.
In round 4 ANZAC lands three planes on the US carries during combat movement. By ANZAC 5 those three fighters are already corrupted. If you open the game file at the start of ANZAC 5 or any point thereafter, you’ll noticed that if you try to move one of those fighters, the little movement space counter says 1/0 rather than 1/4, as in, these fighters have 0 total movement capacity. (although oddly you can still move them)
Interestingly, in round 5, two of the fighters attacked undefended transports, an action which is an auto-kill and doesn’t require an actual dice roll and disguises that they were already corrupted at that point.
The one fighter which came from Queensland on round 5 to join the fleet is uncorrupted, which is why it’s the only one able to attack Sumatra on round 6.
I tried for a while, but I’m still unable to replicate the error. Hopefully that narrows down the origin though.
BTW I pulled the older game files from here: