I have been having the same issue... (sh4 1.5)
Things were going great till about the end of my third or fourth patrol. Never had a problem with TC. Now even at very low TC (256) SH4 just freezez up. Not sure but I think it might be a particular date (I'll have to test it).
Anyways its been such a love/hate relationship with SH4..
. Personally I have never played a game THIS flawed and I really think UBI owes support on something so bugged.