Troubleshooting · updated 2026 · ~4 minute read

Why a follower's position doesn't match the leader

MirrorFill mirrors the leader's net position onto each follower — delta-exact, ordering only the difference after every fill. When a follower differs from what you expect, it's one of a short list of causes, and the engine usually knows about it before you do.

First: is the difference configured?

A follower is supposed to differ when you told it to. A 0.5× multiplier holds half. An exact quantity holds N contracts whatever the leader does. Reverse copy holds the opposite side. Mini↔micro cross-sizing holds MES against an ES leader — different contract, different count. Check the rule before suspecting a fault.

What an amber "Catching up" row means

On the Trade Desk positions table, each follower row reads Mirrored or Catching up. Amber means the follower's actual position differs from its target right now — and the engine has noticed. It is a status, not an alarm.

Causes, ranked by how often they're the answer

1. An order is still resting. Follower mirrors go out as marketable-limit orders. In a thin moment one can sit unfilled. It keeps working at its price; when it fills, the row goes back to Mirrored.
2. A rejection. The broker refused the mirror — margin, session, permissions. Check Order history → Rejected for the broker's reason.
3. An expiry write-off. If you set an order expiry, an unfilled mirror was cancelled and the missed quantity written off — deliberately never re-chased at market. The follower runs that much smaller for now.
4. A manual trade on the follower. Anything you place directly on a follower account is drift to the engine, and it will be corrected.
5. A locked account. A risk-limit breach or manual lockout stops copying and keeps the position where it was.

What fixes what

Reconciliation corrects drift in a quiet market window — but it deliberately skips accounts with a resting order, locked accounts, and paused rules. So a resting mirror is left to fill or expire, and a locked account stays put until you unlock it (it re-syncs on the next pass). Write-offs clear on their own when the leader goes flat or reverses — that ends the episode.

Quick answers