Zigbee2MQTT fails to connect to SONOFF ZBDongle-P on Home Assistant OS

What happened?

I am using a SONOFF ZBDongle-P with CC2652P and zstack.

Zigbee2MQTT repeatedly fails with:

Failed to connect to the adapter (Error: SRSP - SYS - ping after 6000ms)

What has already been tested:

Different USB ports
Other USB devices disconnected
ZHA is not installed
SONOFF Dongle Flasher stopped and autostart/watchdog disabled
Coordinator firmware 20250321 tested
Coordinator firmware 20240710 tested
Fresh Zigbee2MQTT installation with completely new data directory
Zigbee2MQTT 2.12.1 also tested: same error
Full Home Assistant backup from several days earlier restored: same error
HAOS downgraded from 18.2 to 17.3: same error
No relevant USB/CP210x disconnects or errors in dmesg while Zigbee2MQTT fails

Important finding:

With Zigbee2MQTT stopped, the coordinator can be accessed directly from the Home Assistant Linux host.

Sending the ZNP SYS ping frame:

FE 00 21 01 20

returns the valid response:

FE 02 61 01 59 06 3D

This also works immediately after Zigbee2MQTT has failed.

The same dongle was also tested with Zigbee2MQTT natively on Windows using COM5, zstack, 115200 baud and the same firmware. Zigbee2MQTT starts successfully there and works repeatedly.

On Home Assistant there was also one occasion where zigbee-herdsman successfully communicated with ZNP and performed NV reads/writes, but later failed with:

SRSP - APP_CNF - bdbStartCommissioning after 40000ms

Subsequent starts went back to the SYS ping timeout.

A socat test was also performed. Socat successfully opened the physical USB device and created a PTY, but Zigbee2MQTT then remained at:

Starting Zigbee2MQTT...

The Home Assistant add-on container itself remained running.

Because direct ZNP communication on the same HAOS machine works, and the same dongle works with Zigbee2MQTT on Windows, I suspect an issue with serial initialization / zigbee-herdsman / the Home Assistant add-on environment rather than faulty coordinator hardware.

Is there anything else I can test or any known issue affecting CC2652P / CP210x serial initialization on current Home Assistant OS?

What did you expect to happen?

No response

How to reproduce it (minimal and precise)

No response

Zigbee2MQTT version

2.13.0-1

Adapter firmware version

20240710

Adapter

ZBDongle-P

Setup

Environment:

Home Assistant Core 2026.8.3
Supervisor 2026.07.5
Home Assistant OS 18.2
Zigbee2MQTT 2.13.0-1
zigbee-herdsman 10.8.0
SONOFF ZBDongle-P / CC2652P
CP210x USB serial adapter
Baudrate 115200
Adapter: zstack
RTS/CTS disabled

Device database.db entry

No response

Debug log

[20:44:49] INFO: Preparing to start...
[20:44:49] INFO: Socat not enabled
[20:44:49] INFO: Starting Zigbee2MQTT...
Starting Zigbee2MQTT without watchdog.
[2026-08-22 20:44:50] info: z2m: Logging to console, file (filename: log.log)
[2026-08-22 20:44:50] info: z2m: Starting Zigbee2MQTT version 2.13.0 (commit #unknown)
[2026-08-22 20:44:50] info: z2m: Starting zigbee-herdsman (10.8.0)
[2026-08-22 20:44:50] info: zh:zstack:znp: Opening SerialPort with {"path":"/dev/serial/by-id/usb-ITead_Sonoff_Zigbee_3.0_USB_Dongle_Plus_c217ee58319eef11b6d4cfa661ce3355-if00-port0","baudRate":115200,"rtscts":false,"autoOpen":false}
[2026-08-22 20:44:50] info: zh:zstack:znp: Serialport opened
[2026-08-22 20:44:50] info: zh:zstack:znp: Writing CC2530/CC2531 skip bootloader payload
[2026-08-22 20:44:51] info: zh:zstack:znp: Skip bootloader for CC2652/CC1352
[2026-08-22 20:45:10] error: z2m: Error while starting zigbee-herdsman
[2026-08-22 20:45:10] error: z2m: Failed to start zigbee-herdsman
[2026-08-22 20:45:10] error: z2m: Check https://www.zigbee2mqtt.io/guide/installation/20_zigbee2mqtt-fails-to-start_crashes-runtime.html for possible solutions
[2026-08-22 20:45:10] error: z2m: Exiting...
[2026-08-22 20:45:10] error: z2m: Error: Failed to connect to the adapter (Error: SRSP - SYS - ping after 6000ms)
at ZStackAdapter.start (/app/node_modules/.pnpm/zigbee-herdsman@10.8.0/node_modules/zigbee-herdsman/src/adapter/z-stack/adapter/zStackAdapter.ts:95:27)
at async Controller.start (/app/node_modules/.pnpm/zigbee-herdsman@10.8.0/node_modules/zigbee-herdsman/src/controller/controller.ts:146:29)
at async Zigbee.start (/app/lib/zigbee.ts:70:27)
at async Controller.start (/app/lib/controller.ts:117:29)
at async start (/app/index.js:156:5)

Notes

No response

Start at zigbee-herdsman’s zStackAdapter.ts:95 and compare the logged serial initialization with the direct ZNP ping and the successful Windows run. Reproduce on the Home Assistant add-on using the stated firmware, baud rate, and /dev/serial/by-id path. Done means identifying and fixing the cause of the SYS ping timeout so Zigbee2MQTT starts reliably on this setup.