that's weird Alkay, so is the perpendicular line below your finger a join in the timber or a line where you stopped sanding ?
my guess is the TO didn't cure properly, still waiting to hear how long you let it cure before sanding
EDIT just read your edited post so Saturday was the last coat, you need to wait at least a week probably 2 weeks in winter before wet sanding. Where do you live Alkay ?
DB's rule is let any finish cure for minimum 3 weeks before wet sanding and polishing