I am not certain what you are looking at, but be sure that you don't just arbitrarily open files. Early 1944 would be the 43a series of files. All three of these grabs are "43a_Jap_" files, in CoastalTraffic, Convoys, HarborTraffic, Merchants, TaskForce and TroopConvoys combined into one. The CoastalTraffic and very little of the HarborTraffic shows in these pics:
Rosegarden:
Corridor II:
and Palau area:
Now, the Rosegarden is definitely "shy" on traffic, as compared to the others, but those are some high-spawn-rate groups. Corridor II (two) is a rather high-density area, and Palau should be teaming. By the time summer (after June 1944 aka: 44a files) comes along, things will start to get scarce in those areas.
Things to look for would be "is the mod activated correctly?". Do you get an FotRSU splash screen as the game starts, like the one below in my "signature" here? Did you empty the Save folder after activating FotRSU? Failure to do so would result in a partially activated mod with odd traffic patterns. Have you been shelling out to Windows, whether purposeful, accidental or Windows-induced? Doing so can result in graphic and sound anomalies, as well as eventual bad Save data, which of course, can result in odd traffic patterns. Also, bear in mind that (especially in the Rosegarden) it might be a while before a group would come along, and if you're in the wrong spot, you would never know it. You don't have to keep your radar on all the time, but be certain you have it set to reach out beyond the "default" setting, which is NOT very far, and that you have it on "Sweep". While the hydrophone does work on the surface, it works better submerged on electrics at slow speed, so do a dunk and spin every once in a while, looking for sound contacts. You should not have a bit of trouble finding something off Palau. Patience and rig for depth charges are required, being mindful of the shoals and the 100 fathom line...
