I'll bet it has to do with leaving Pearl and crossing the date line. I have always been in the Asiatic Fleet until my latest patrol. And today, upon firing my first torpedoes of the patrol, I noticed the 20 deg bug.
If the date line can screw up the attack map torp tracking, it can probably screw up other torpedo issues.
Please speak up if you have seen this behavior WITHOUT crossing the date line.
Devs and UBI...