Check if the CO is sending clocking as well as the Samsung. I just conquered a Nortel rebooting with the exact same scenario.
The system would work fine and then no calls except intercom. This would happen about once a week, sometimes more days, sometimes fewer days. Rolled the DTi card for the PRi circuit with no effect.
Finally I set the whole problem on Telepacific and insisted on a monitor until it failed telling them this HAD to be slippage in their on prem Adtran or repeaters or central office, it was NOT the Nortel.
That gave them a clue where to look and when we talked again I asked the TP teck if he was possibly sending clocking. On looking at specs, he said "Yes."
What is going to happen if both your Samsung and the CO send signaling, ERRORRS. Enough errors and the circuit dies, power down, it starts up again, syncs, and all is well.
Now TP wants US to turn off clocking and I said NO. We never asked them for clocking, our switch provides it, and it would be a service call for our customer.
I can't be positive that dual clocking is your problem, but the symptoms are identical. And, in each case for both of us, rebooting the system brings it back up for days.
I haven't been on for a while and I'll be on sporadically, I've been dating a Conservative rabbi and I'm moving 100 miles to be with her and help her set up a new synagogue. She is BRILLIANT, and so much more fun than doing phone work.