SONOFF MINI-ZB2GS-L (1.0.4 / build 4100): relay powers up OFF after mains loss, `startUpOnOff` accepted but not applied

What happened?

Both relays on a SONOFF MINI-ZB2GS-L come up OFF after every mains interruption, regardless of power_on_behavior. The write to startUpOnOff succeeds and the device stores the value; it is not applied at startup.

Detach relay mode is enabled on both channels and the load is a set of Hue bulbs, so the relays are meant to stay closed permanently.

Device: SONOFF MINI-ZB2GS-L, firmware 1.0.4, build 4100, date code 20250821. detach_relay_mode ENABLE on both channels, external_trigger_mode edge, latching wall switches.

The relays boot open. In all four cycles below, the first state reported after boot is off; there is no intermediate on.

The relay is physically open, not misreporting. After cycle 2, commanding a downstream Hue bulb produced no response and its state was never updated; the bulbs have no mains power.

The write is accepted. Changing power_on_behavior (on to previous) completes with no error on zigbee2mqtt/bridge/logging. delayed_power_on_state and delayed_power_on_time in the eWeLink cluster are also accepted and reported back by the device, and likewise have no effect on power-up state.

detach_relay_mode is unchanged across cycles, reading ENABLE/ENABLE before and after each.

What did you expect to happen?

With power_on_behavior: on the relay closes at power-up. With previous it restores its pre-outage state, which was on in every cycle below.

How to reproduce it (minimal and precise)

Four mains cycles at the breaker, ~60 s off. Both relays confirmed on immediately before each.

#	power_on_behavior	delayed_power_on_state	Result
1	l1 on, l2 on	disabled	both off
2	l1 on, l2 on	enabled, 1 s, both channels	both off
3	l1 previous, l2 on	disabled	both off
4	l1 on, l2 on	disabled	both off

All cycles 2026-09-08; l1 reported off first in each, l2 six to seven seconds later. Cycle 3 sets a different value per channel in one power cycle. Cycle 4 was run on Z2M 2.14.1-1, cycles 1-3 on 2.12.1-1.

Zigbee2MQTT version

2.14.1-1

Adapter firmware version

20240710

Adapter

SMLIGHT SLZB-06 (core firmware v3.3.1)

Setup

Zigbee2MQTT Home Assistant add-on 2.14.1-1, running under Home Assistant 2026.6.3 in a VM on an x86-64 NAS with an Ubuntu Server host.

Coordinator is a SMLIGHT SLZB-06 attached over Ethernet (connection mode eth), so Z2M reaches it over TCP rather than USB.

Device database.db entry

{"ieee_address":"0x403802fffe0f329f","type":"EndDevice","network_address":36631,"power_source":"Mains (single phase)","manufacturer":"SONOFF","model_id":"MINI-ZB2GS-L","software_build_id":"1.0.4","date_code":"20250821","supported":true,"disabled":false,"interview_completed":true,"endpoints":{"1":{"bindings":[{"cluster":"genPollCtrl","target":{"endpoint":1,"ieee_address":"0x00124b002e1e03c1","type":"endpoint"}},{"cluster":"genOnOff","target":{"endpoint":1,"ieee_address":"0x00124b002e1e03c1","type":"endpoint"}},{"cluster":"customClusterEwelink","target":{"endpoint":1,"ieee_address":"0x00124b002e1e03c1","type":"endpoint"}}],"configured_reportings":[{"cluster":"customClusterEwelink","attribute":"externalTriggerMode"},{"cluster":"genOnOff","attribute":"onOff"}],"clusters":{"input":["genBasic","genIdentify","genGroups","genOnOff","genPollCtrl","haDiagnostic","manuSpecificAmazonWWAH","customClusterEwelink"],"output":["genIdentify","genOnOff","genOta"]}},"2":{"bindings":[{"cluster":"genOnOff","target":{"endpoint":1,"ieee_address":"0x00124b002e1e03c1","type":"endpoint"}},{"cluster":"customClusterEwelink","target":{"endpoint":1,"ieee_address":"0x00124b002e1e03c1","type":"endpoint"}}],"configured_reportings":[{"cluster":"customClusterEwelink","attribute":"externalTriggerMode"},{"cluster":"genOnOff","attribute":"onOff"}],"clusters":{"input":["genBasic","genIdentify","genGroups","genOnOff","customClusterEwelink"],"output":["genIdentify","genOnOff"]}}},"definition_model":"MINI-ZB2GS-L"}

Debug log

No response

Notes

Koenkk/zigbee-OTA contains one ZB2GS image, images/Sonoff/mini-zb2gs_v1.0.7.ota (fileVersion 4103, manufacturerCode 4742, imageType 68), which is the neutral MINI-ZB2GS. This device is at 4100 and is offered no update, so there is currently no OTA path for the -L variant.

The device entry above is from zigbee2mqtt/bridge/devices rather than database.db.

Start by tracing the MINI-ZB2GS-L device definition and the handling of power_on_behavior, then compare it with the reported bridge/devices entry and customClusterEwelink attributes. Done means power_on_behavior on and previous produce the expected relay state after mains cycles, including with detach_relay_mode enabled; verify the behavior against the four reproduction cases.