Short answer
A copy is skipped when it breaks one of your limits or fails a safety check, for example a failed rug check, your max per token, a price impact that's too high, or one-tap trading being off. The reason is shown in your copy history.
Common reasons include: the token failed the rug check (always skipped) or had no check yet with “skip unchecked tokens” on; you'd already reached your max for that token; copying had paused at your loss limit; the trade would have moved the price too much; your wallet didn't have enough balance or SOL for fees; or one-tap trading was off, shown as needing your wallet.
Skips are the limits working as intended. Your result will differ from the trader's because of them, and that's usually a good thing.
See the checks for yourself
18+ only. Self-custodial: you keep your keys. 0.45% per trade, no minimum. Memecoins can go to zero.