Okay - now I'm not sure whether this messes with the bug report side of things (Sorry to Cranium Muppet, MatRopert et al if it does) - but testing this in a controlled environment I hope highlights the mechanic without AI decisions confusing the story. Assuming I haven't messed things up/misunderstood things (quite possible - I'm a bit brain-dead today), this looks like a critical "must-fix" bug (although obviously that's just my take - you should triage the bugs as appropriate at that end - I can't see what other tasty bug morsels you have on your plate, and I might make a horrible bug prioritiser even if I could
).
Version: 1.11.4.45cf
Checksum: 6c71
DLC - all except music packs with vocals
Repro steps:
1) Load attached save as ENG - do not start time running.
2) Open the console, and enter "AI" to stop the AI doing things to make it hard to work out what's going on.
3) Observe that as ENG you're at war with France.
4) Press F2 and click on the fleet in the channel, and observe they are set to "always engage", as per the first screenshot below.
5) Open the console and change tags to FRA
6) Click on the FRA fleet in the channel and observe, as per the second screenshot, they're set to "always engage" as well.
7) Hover over the detection bar for the ENG task force to get a look at their detection stats, and as per the 3rd screenshot below observe that despite wanting to engage at all costs, the British have a negative detection chance.
8) Let time run until 18 Jan (or so) - observe that two fleets that really want to go at it, are taking days to find each other, in the English Channel.
9) tag back to ENG, and hover over the detection stats, and observe as per the 4th screenshot, and note that from the ENG point of view, despite both fleets wanting to come to action, the ENG detection chance is negative, driven by the French having a negative detection chance, and the large speed differential in favour of FRA.
10) Let time run again, until 25 Jan - observe, as per the 5th screenshot below, that the ENG detection chance never gets above 21% - so the ENG fleet would never be able to find the FRA task force, despite both wanting to have at it.
I'd also argue the rate of FRA spotting is far too low, even if ENG didn't want to come to action, given the speed differential - three or so months to spot the enemy is a bit on the long side (given the size of the sea zone at least).
Screenshots in a spoiler because there are five of them: