Engine stuttering/dying and loss of accelerator

I had recently bought a 1998 Gen 3 Subaru legacy (BH5) with 190k Kms/ 118k Miles on it, for the first month it ran perfect with zero issues. Suddenly one day I started up the car as I was reversing out I could hear and feel the engine cylinders become more erratic and slow down until 3 seconds later the entire car died. I cranked the car again and then as if nothing happened I drove home without a hitch.

After the first incident, a few days later while I was driving it occurred again, the engine started to stutter, and would slowly die – prior to the engine going out 3-5 seconds before, the accelerator pedal would become unresponsive, no matter how far down I pushed there would be no acceleration at all as if I hasn’t even touched the pedal. Then again after the car dies I restart and its usually normal again. These incidents would begin to occur more and more until a week later now it happens ~ every 2 days.

I found a video of my exact same car, this is a identical 1:1 of how the engine behaves, moves and sounds on mine (video at 0:50 – 1:30)

https://youtu.be/uUMFOQcvKtg?t=51

I checked the fuel fuse, it was fine but I replaced it anyways, had a battery and alternator check and they were fine. I took it to a mechanic who took it for an entire days test drive along roads and hill and it wouldn’t play up even once. He checked the engine and said the sparks and leads were all good, he did a scan and it showed up with zero codes. so now I’m left wondering what it could be, my only guess is the fuel pump or filter has an issue as I’m told on many older cars they don’t sensor codes for it – but when I suggested it to the mechanic he said probably not but didn’t give a reason why and just said bring it in again.

Anybody have any thoughts on what might be going on?