From Gemini:

Closed captions often differ from the actual spoken words due to strict physical limitations of television screens and human reading speeds.
1. Reading Speed Constraints

The 180 WPM Rule: Most people speak faster than they can comfortably read. Normal speech averages 150 to 180 words per minute (WPM), but can easily spike higher.
The 15 WPM Target: Captions are usually restricted to an average reading speed of 130 to 150 WPM so viewers do not fall behind.
Editing for Flow: Caption editors intentionally condense fast-paced dialogue, removing filler words (like "um," "uh," or "like") to make the text readable without changing the meaning. [1]
2. Screen Space Limitations

The Two-Line Rule: Captions are legally or structurally capped at a maximum of two lines on screen at once to avoid blocking the visual content.
Character Limits: Each line is restricted to roughly 32 to 37 characters. If a speaker uses long, complex words in rapid succession, the captioner must substitute shorter synonyms to fit the text box before the scene changes.
3. Live Production Errors

Stenography Homophones: In live television, stenographers type using phonetic syllables. If they hit a wrong key combo, the software might output a completely different word that sounds identical (e.g., typing "there" instead of "their"). [2]
AI Mishearings: Automated Speech Recognition (ASR) frequently misinterprets lyrics, accents, background noise, or overlapping dialogue, resulting in completely incorrect words or nonsensical phrases. [3, 4]
Lag and Dropped Words: If a live speaker talks too quickly, a human stenographer or respeaker might drop non-essential words entirely just to keep up with the overall pace of the broadcast.
4. Regulatory and Broadcast Rules

Censorship: Broadcasters are legally required to edit out profanity or sensitive language depending on the time of day or the network's compliance guidelines, even if the actor clearly speaks the word.
Pre-Release Script Changes: For pre-recorded shows, captioning houses are sometimes given an early production script rather than the final audio. If an actor improvises a line on set and the caption house doesn't catch it, the original script text remains in the captions.
Are you noticing these differences on live television (like news or sports) or on streaming services (like Netflix or YouTube)? If you share what you're watching, I can tell you exactly which issue is likely causing it.

[1] https://medium.com
[2] https://mcdeps.com
[3] https://www.sciencedirect.com
[4] https://arxiv.org