A sudden reach drop feels personal. It usually is not. Work through these before reaching for a conspiracy.
The likely explanations
1. Regression to the mean. If a recent post overperformed, the next few will look bad by comparison. This is the single most common cause.
2. Format change. Switching from the format the platform is currently pushing to one it is not will cut reach immediately, regardless of quality.
3. Posting rhythm change. A gap of a week or two, or a sudden burst after a quiet period, both disrupt distribution.
4. Topic drift. If your recent posts sit outside what your audience subscribed for, engagement rate falls, and distribution follows.
5. Seasonality. Whole categories go quiet at predictable times. Compare against the same weeks last year, not last month.
6. A restricted tag. Rarer than people think, but real. Check any unfamiliar tag you recently added.
7. Platform-wide change. Check whether other accounts in your niche are seeing the same thing. Frequently they are.
8. The content genuinely was not as good. Uncomfortable, and often correct.
How to actually diagnose it
Compare rolling thirty-day averages, not individual posts. Individual post variance is enormous and tells you nothing. If the thirty-day average is flat, nothing happened.
What not to do
Do not overhaul everything at once. Changing your format, cadence, topic and tags simultaneously means you learn nothing from the result. Change one variable, wait two weeks, look again.