You have your mod list in a bit of a mess with some over-writing each other... Try doing it this way:
Generic Mod Enabler - v2.6.0.157
[C:\Spiele\Ubisoft\MODS]
Nihon Kaigun v1.3a_FotRSU
Nippon_Maru_v1.9b_FotRSU
Combined Roster Add - Enables Nihon Kaigun + Nippon Maru to be installed together with shared rosters.
450_MoonlightzSonarLines
399_NoScrollNavMap
525_StickieCamera
801_UMark Smaller
Fleetboat_Interior-Officers_Quarters_FOTRSU_v1.7_EN
FI-OQ_FotRSU_v1.8f_upcPatch
Improved Stock Environment_v3_TMO&RFB
#1 ISE New clouds+Waves
#2 ISE Realistic Colors
Japanese DD skins correction - Historical
FOTRSU_1.8_SUB_SKINS_IN_4k
Now, the ISE and #1 and #2 might all be incompatible with FotRSU, in spite of FotRSU being based on TMO v1.7 years ago. There have been changes to the mod, and any environmental mod can influence the sensors for ships and your sub, so if you notice any short-sighted planes or ships, that's what is probably the cause. Also note that some of the environmental mods from that time period were included in FotRSU, and you might be overwriting stuff already in there... I am not familiar with the DD Skins mod, and it probably does not cover all the DD in the mod, and some may not fit the changes done to the mod since it was first built, so if you notice some IJN DD that look odd, that would be the issue. The "Combined Roster" is a mod included in the MODS folder with Nihon Kaigun and Nippon Maru, and is needed to allow both mods to work together inside FotRSU.
Other than that, after you re-arrange things, be certain to delete the Save folder, which would be "C:\Users \UserName \Documents \SH4" by default, unless changed by the use of MultiSH4. You can also use the Windows side dialog in Explorer, but be aware that there is a difference in Windows 11 (and sometimes 10, dependent upon config), where the UserName directories are ~different~ from the shortcut directories for some odd, Windows reason... Case in point is this Win11 laptop of mine, where the SH4 directory is NOT under UserName, but is rather a "shared" directory that I can only find from the side dialog window, as here:
YMMV... unfortunately
