Quick fix: Drop only the cable stitches, let them unravel to the missed row, re-cross with a cable needle, then work back up with a crochet hook.
What you are seeing
A section that should twist into a cable sits flat as plain stockinette. The cable is missing its cross at one row.
Why it happens
- Lost count and worked the cable row as plain stockinette
- Miscounted plain rows between cable crosses
- Distracted mid-row
Fix it now
- Find the exact row where the cross should have been.
- Drop only the cable stitches off your needle. Let them unravel down to the missed row.
- Place the left-group stitches on a cable needle, hold to front (or back for a back cross).
- Use a crochet hook to work the right-group stitches back up their ladder rungs.
- Then work the left-group from the cable needle back up their rungs.
- Return all stitches to your needle.
Prevent it next time
- Use a sticky note tally for plain rows between each cable cross
- Place a stitch marker on the cable row
- Insert a lifeline just before every cable row