Google made an announcement that they are going to be adjusting how Dynamic Search Ads are triggered over the next few months.
Ultimately, they want to improve ad relevance on search queries. This is from that announcement:
For example, ads that point to a landing page about iced coffee makers will be less likely to show for less relevant searches like “iced coffee.”
Google said that once the updates begin rolling out, performance could fluctuate. Basically, keep an eye on the search terms report vigilantly with DSA campaigns during the transition period to see how query matching is affected.