TFs that can't be intercepted
 

Bound for the Philippines out of Surabaya at the end of February, one can either go up the Celebes Strait or up the western Borneo coast. Either route can lead to an invasion TF with small transports led by CAs. Following a day or two behind is another TF, which appears only as a map contact. I've tried repeatedly to intercept one of these, including taking station at the Celebes bottleneck, but it never works. I've also seen this behavior in another career with the Huge Ocean Liner (to date I've had more encounters with the Flying Dutchman than that ship) only 20 km or so away.

What's the rationale behind this? And does this happen in other scenarios?

There is a setting for the groups in a file that if enabled, tells the game how often to report a group, and also how long to wait before reporting said group. Depending upon the mod and group, some groups will zig zag every 10nm or so, or maybe 24nm, so there is that variable. There is also complete changes of course from say a southeaterly course, to a south-southwestern course. So, you might have an old report, that is completely inaccurate by the time you act on it. Imagine the coastwatcher that is watching the passage of the group out of the harbor, running to his radio, and the enemy shore patrol comes along, and the watcher can't x-mit his report for hours... or maybe its an "Ultra" situation, and the cracked code info on the group is deemed "low priority" and doesn't make it to the translator / intelligence officer for two hours or more. Again, old info to you that might be completely inaccurate by the time your receive it. This is the main reason not to chase those reports. However, if you do find them, they'll talk about your encounter for ~years~ in the officer's club... :salute:

yes, definitely.
i have been within 10 miles of an unspawned convoy/TF when its position was automatically reported and i never made contact.
it was and still is a mystery to me.
log it and sail on...is all i can say.
:Kaleun_Salute:

Those are all excellent points; however, I think something else is going on in the particular case of the invasion of Java. The circumstances are unusual yet the same in either zone: one uncharted TF that the player discovers via proximity and can defeat using extremely aggressive tactics, and one charted TF following that can't be located, even in multiple attempts over several careers.

I assumed I had just missed the second eastern convoy previously, but once I finally bit the bullet and took the western route (I avoid the Java Sea whenever possible) and discovered the same pattern, it changed my mind. That's when I blockaded the narrowest point in the Celebes Strait and watched the phantom TF appear first off Davao, then only a few dozen km NE of my position. I was slightly to the left of the center of the Strait, in line with their predicted approach, but they never appeared on my SJ-1 scope, despite waiting several days. I repeated this experiment an equal distance on the other side of the strait. Nothing.

Using realism factors of around 30%, I can contact a fleet TF in at least 80% of patrols, even in ridiculous times like early August 1945. These phantom TFs though? Never.

I suspect it may have been intended to give the player a chance to do his part against the invasion while maintaining its inevitability.

One suggestion, use the mission editor to open EastAsiaCampaign.mis and the assorted 42a-b-c task force missions, see if you can find the phantom task force and trace the waypoints. In many cases the paths have alternate paths with random percentages, so it's possible for any given group to suddenly change direction and take a different route.