TIMEOUT — Error Class DEVICE, code TIMEOUT

No response arrived within the APDU timeout. On BACnet/IP this usually means broadcast or routing trouble rather than a dead device.

Start free BACnet/IP → canonical

Diagnosis

When you hit this

The device is on a different subnet and no BBMD is configured, so broadcasts never reach it.
Foreign device registration expired.
APDU timeout too short for a device on a slow MS/TP segment behind a router.

Resolution

How to fix it

Check BBMD configuration
BACnet/IP relies on broadcasts that routers do not forward. Each subnet needs a BBMD, and its broadcast distribution table must list the others.
Raise the APDU timeout for MS/TP
A device behind an MS/TP router can be an order of magnitude slower than one on Ethernet. Defaults tuned for IP are too short.
Re-register as a foreign device
Foreign device registration has a lease. If it lapses, unicast works and broadcast discovery does not.

Normalization

What Forge does about it

This is a transport failure, so there is nothing for Forge to normalize: the reading never arrives. What Forge does is refuse to let the gap look like good data. The read-time dropout check flags a field that fell to zero and recovered as a communication glitch rather than a real measurement, and the stuck-sensor check fires when a value repeats for 20 consecutive readings — which is what a cached or last-known value looks like after a link drops. Forge does not retry or reconnect for you; that is your client's or your gateway's job.