Were they for sure part of that particular Task Force? If so, open your MIS file of course, and check the route. I've found a few (not in RSRDC) that the group is routed near dry land, leaving two or three vessels that have to "fend for themselves" and attempt to get around the obstacle. They get separated far enough (I've not seen that happen), they may lose their guidance "brain"... Also, there was a Task Force stuck in Truk when we were having all of our fun with that a few months ago, and the ships that got separated from the others in the group would hang back and "wait" on their brethren to get through the traffic jam. Were the CA maybe the "leader" of a Task Force? Then there is always the chance that the routing looks good, until you "merge" the minefields file in, and you discover that half of a group is lost to a minefield that they've traveled through - lengthwise...
- if there's a ReadMe with the ISP, see if they touch the CA. I'm thinking (scary) that they don't, but I don't remember... you could also just look at the files in the mod itself and see if they noodle with any...