Winning campaign that suddenly tanks

I am running a PPV campaign for an international lead offer.

Landing page generates CTR at 7-12% constantly. I target very relevant URLs.

The first few days, it converted like 9% of the clicks, resulting in at least 200% ROI. Very nice.

But suddenly in just 3 days, things changed. From 9% to 2%, 1%, 0.5% and now. Zero conversions for hundreds of clicks!

This offer has been running for a year so I know it is working.

Have you experience this before? What do you suggest? Should I just kill the campaign and move on? I thought I got a winner...

I am not using PPV traffic. But i have other similar situation like this . If the situation continues, try twist your landers, or targeting urls.
If no working try other offers.

It may be that the advertiser bounces leads. Try another offer and see if your CTR grows back.

It did. After trying new offers, the response was back for a day, then the same thing happened again.

Very frustrating as I'm sending paid traffic there.

Looks like they don't like your traffic. I can only think of using multiple CPA networks and just rotating offers between them.