Explanation
The term is used far more often than the phenomenon occurs. Normal short-form distribution is extremely variable, and a run of poor-performing posts is the expected behaviour of the system rather than evidence of intervention. Most self-diagnosed shadowbans are a format that stopped working or a seed audience that did not connect.
What genuinely does reduce reach is documented and checkable: another platform's watermark, content that brushes the guidelines, engagement bait, and repeated deletion and reposting. Those are worth auditing before reaching for an unfalsifiable explanation.
The common mistake
Changing everything at once in response to a suspected shadowban. It guarantees that whatever recovery follows teaches you nothing, and recovery usually follows regardless.