Must admit, I cannot come up with an answer or explanation for that question 🤷♂️. All I know or can say is I changed nothing.
But dig this... (not to add to the mysteries or anything)
Just went to the IB. Control Panel opened! I set it to 24H & d/m/y.
Told it to Show seconds, which it did AND did not switch to AM/PM.
Told it to Abbreviate and it did not switch to AM/PM.
Told it to do both and it did not switch to AM/PM.
So, it is not doing it in either IB or retail.
Cheers,
Drew