This may also be a game issue.
Are you saving inside 20km of port? I reccomend not to.
Come into port outside of 20km on a fresh save. Make sure you are not spotted or even above water if it is daylight. This is important.
It sounds to me like you had been previously spotted and then picked up again due to the DDs already being in an agressive state.
I forget really, but i think agressive AI will be still aggressive when you reload a game that they werent hostile in previously if within 20km.
Saving is bad all around in this game. Some recommend to only do it completely stopped and surfaced with no contacts or land <20km away not before laborday and without reporting to your Subpac
GLHF you will get a lotta mileage out of this game starting at 15%