I do not know how many seconds you define “a couple” to be (strictly speaking, “a couple” would be 2) but to go from 70 to 30mph in two seconds is a massive amount of deceleration. If that is truly happening that is very dangerous, the equivalent of suddenly applying the brakes at full force. If my Teslas did that I would not ever drive them except to get them to my local service center immediately. That is not acceptable behavior while on EAP.
You do not say if you have had Tesla service look at the car. Why not? Submitting a bug report through the car is not going to solve the issue.
That said, I suspect you are exaggerating, something people often do when describing a problem. An oft reported EAP issue on TMC is sometimes described as “shadow braking”: the car brakes on the highway for no apparent reason, slowing about 5-10mph and then resuming. Some people believe this happens because the shadow cast by an overpass, for example, confuses the car into thinking it is an obstacle.
Over the years I have had that happen multiple times; the car rarely decreases speed more than 5mph and then resumes or I press the accelerator to resume speed before the car does. I have not had it happen for months now; it think the issue is much less frequent than it ws before.
You should take your car into Tesla service for a check up.