Your retargeting set (people who visited your site in the last 30 days) is showing your ads to the same people about 7 times per week. A week ago it was 5. Click rate dropped 38% in the same window.
In plain English: you've shown your retargeting audience the same ad until they tuned it out. You're now paying more per click for the people least likely to buy. Either widen the audience (60-day or 90-day window) or refresh the creative — usually a single new variation drops frequency back to under 2.0 within a week.