Short answer
Most likely an auto-applied recommendation. Google Ads can be set to apply its own recommendations automatically, including raising or lowering target ROAS and CPA. The change history shows them as Recommendations Auto-Apply rather than a person. They are opt-in, often switched on years ago, and can be turned off in the Recommendations page.
What it looks like
A campaign that was delivering starts to slow down. Nobody changed anything. In the change history there is an entry, and the user is not a person: it reads Recommendations Auto-Apply.
On one Shopping account, auto-apply raised Performance Max's target ROAS to 35.84 when the campaign was actually achieving 29.2. A target set above what a campaign achieves throttles it, and delivery falls off over the following days while everyone looks for a problem with the ads.
How common it is
When we checked the Google Ads accounts we manage, half had the full set of 21 auto-apply types switched on, including every bidding-target type. They had been opted in at some point, usually during onboarding or a Google rep call, and nobody remembered.
One store had 21 enabled while its tracking was also broken, so Google was applying bid changes based on conversion numbers that were not real.
Which ones matter
The dangerous ones change bidding: set target ROAS, raise target CPA, lower target ROAS, set target CPA. They can overwrite a target you set within days, with no name against the change.
Others add keywords, broaden match types or rewrite ads. On a Search account those change what you pay for. On a Shopping or Performance Max only account they mostly have nothing to act on, which is why switching everything off there loses nothing.
How to switch them off
In Google Ads, go to Recommendations, open Auto-apply, then Manage. Deselect all on each card and save. Recommendations still appear for you to review by hand; they just stop applying themselves.
Check afterwards. We have seen one type still reported as enabled through the API after the screen showed zero, so confirm in the change history over the next week that no Auto-Apply entries appear.
Do this before fixing anything else
If you are about to reset a target, restructure campaigns or fix conversion tracking, switch auto-apply off first. Otherwise Google can quietly undo the fix, and you will spend a week diagnosing a change nobody made.