I can almost promise you its SH3 commanders sabotage and malfunctions option. Your install is fine... SH3C is doing exactly what it is supposed to do.
Dive planes jam, valves fail, engines flood etc in real life, this is why commanders put their boats throught its paces at the start of missions. Test all speed ranges forward and reverse, crash dive, test guns etc.
Your crash dive will work, the ahead flank feature is probably failing. Hit C to crash dive then immediately order ahead full "4". You will crash dive, just slower
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