Quick fix: If you catch it immediately: drop back to the missing yarn over position, create the yarn over by inserting a crochet hook into the bar between the two stitches, and re-knit back up.
What you are seeing
Your stitch count is one lower than expected, and there's a missing eyelet in your lace pattern — a hole that should be there simply isn't. You worked the decrease but forgot to wrap the yarn over first (or after), so the pattern is compressed in that spot.
Why it happens
- Working quickly and forgetting to bring the yarn forward before knitting
- Misreading the chart: yarn over symbol overlooked
- Interruption mid-row causing you to lose your place
Fix it now
- Count stitches and confirm you're one short of expected.
- If you're still on the same row: work backwards (unknit stitch by stitch) to where the yarn over was missed. Bring the yarn forward, slip the stitch back to the left needle, and continue with the yarn over and remaining stitches.
- If you've worked more rows: drop down the stitch column above the missing eyelet. The horizontal bar between stitches at the yarn over row is your material. Use a crochet hook to lift that bar onto the hook as a new stitch (this creates the yarn over retroactively), then re-knit each row back up.
- If the bar isn't large enough to work with: rip back to a lifeline placed before the error.
Prevent it next time
- Before every yarn over: say "yarn forward" out loud as a cue
- After working each repeat, quickly scan for the expected eyelets before moving on
- Use lifelines every 10–15 rows so ripping back is never catastrophic