Wellllll.... v1.4 does NOT have very many mods. If you've activated a mod that is for v1.5, that could explain the issue. There were issues in v1.4 though also, and might be a contributing factor. I do not recall off the top of my head what all was still broke after v1.4.
As for the mods, there are older versions of TMO and RSRDC that worked on v1.4. There is also Fall of the Rising Sun - no "Ultimate" word in that - v2.0 that ran on v1.4 SH4, but it's in German only, though if you can muscle through that, it is really cool, other than some egregious bugs later in the war, that can crash your career, but it is beautiful, and lots of fun to play. Lots of mods have issues in SH4 v1.4 (1.5 for that matter), due to the fact that the Stock game has some issues. For example, February 29th every year, including 1944... June 31st, etc. "Little" things like that...
I'm not sure what you'll find on the site here for download for v1.4, but do an online search and see what you can find. I don't think Webster did his GFO for v1.4, but there are some of his mods here that will work in v1.4, so "Search" for "Webster" in the downloads. Be sure and read the ReadMe stuff for the mods...
It is recommended though, that you at least purchase the
Silent Hunter 4 Wolves of the Pacific: Uboat Add-on. That would allow you to use many more mods, and it does run better than v1.4 - though it does still have little nigglies in it too... I used Amazon in that link, since SubSim gets a "shopping cut" for that link.
- you could also watch for it to go on sale there or elsewhere. Do NOT use the Steam version of the Add-On if you don't have the Steam base v1.3 game...