Similar time frame for me, worked at an ad-tech startup, when retargeting was first becoming a big thing and we were pivoting the startup from the bad business idea it started to to doing retargeting as a demand"-side-platform" (DSP) on ad various exchanges. Tried myself to confirm whether any of it had any positive effect, I couldn't really discern any increase in the click-through-rate (CTR) for various approaches, but I'm not a stats expert, etc. so talked to the founder about how we should employ someone with a stats background. That convo went nowhere, and for that and other reasons I was out the door within a couple months.

That was the era of the ad-exchange DSP bubble. After that I went to work at another company that was on the other side of the exchange pipeline and I could see all these DSPs just plugging away doing their thing and none of it looked (to me) like it was accomplishing much. It was all bottomfeeding off of lower quality inventory but I suspect making big promises to investors.

That startup eventually pivoted a couple more times and sold to a bigger player a few years later, making some money for the founder but I suspect no value to the buyer.