Welcome to Subsim.
Freezing/stuttering while at Time Compression is an indication that SH3 is loading Ships or aircraft with in your subs render range.
It's always evident with low end memory/processor and can actually tell you when possible targets are nearby.
Next time it happens, drop out of TC and conduct a hydrophone check, you should pick up a contact or two.
It's a bit of a game killer but it's the way SH3 works.
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