Update of Salus FC600 failed (Image padding contains invalid bytes)

[mkrle]

I've tried to perform an OTA update on a Salus FC600 thermostat for the first time but faced the following:

[2025-01-12 21:19:03] debug:    zhc:ota: [0x001e5e090904a427 | FC600] Got request payload '{"fieldControl":0,"manufacturerCode":4216,"imageType":44,"fileVersion":3801127}'
[2025-01-12 21:19:03] debug:    zhc:ota: [0x001e5e090904a427 | FC600] Getting image metadata...
[2025-01-12 21:19:04] debug:    zhc:ota: Downloaded main index
[2025-01-12 21:19:04] info:     zhc:ota: [0x001e5e090904a427 | FC600] Getting latest image, meta: {"fileName":"SAL6DF1_003E0029_20221215_1652.ota","fileVersion":4063273,"fileSize":361238,"originalUrl":"http://eu.salusconnect.io/download/firmware/36ab7f9e-6497-4efa-8ece-efb645af9128/FC600_003E0029.tar.gz","url":"https://github.com/Koenkk/zigbee-OTA/raw/master/images/SalusControls/SAL6DF1_003E0029_20221215_1652.ota","imageType":44,"manufacturerCode":4216,"sha512":"c319412eec498d890ec5bc43a9e1ccb0ec0fbc942cff08d867be36718a57e3d9abfa4aa97677214a13e1270c418d14ea40e20b22ea210d3818ed760141b5bb3d","otaHeaderString":"OTA Image File\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000","manufacturerName":["SalusControls"]}
[2025-01-12 21:19:04] debug:    zhc:ota: Downloading firmware image from 'https://github.com/Koenkk/zigbee-OTA/raw/master/images/SalusControls/SAL6DF1_003E0029_20221215_1652.ota'
[2025-01-12 21:19:04] debug:    zhc:ota: [0x001e5e090904a427 | FC600] Image checksum validation succeeded.
[2025-01-12 21:19:04] debug:    zhc:ota: [0x001e5e090904a427 | FC600] Got latest image, header: {"otaUpgradeFileIdentifier":{"type":"Buffer","data":[30,241,238,11]},"otaHeaderVersion":256,"otaHeaderLength":56,"otaHeaderFieldControl":0,"manufacturerCode":4216,"imageType":44,"fileVersion":4063273,"zigbeeStackVersion":2,"otaHeaderString":"OTA Image File\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000\u0000","totalImageSize":361238}
[2025-01-12 21:19:04] debug:    z2m: Update of 'XXX' failed (AssertionError [ERR_ASSERTION]: Image padding contains invalid bytes)
[2025-01-12 21:19:04] info:     z2m:mqtt: MQTT publish: topic 'zigbee2mqtt/XXX', payload '{"fan_mode":"auto","fan_state":"ON","keypad_lockout":null,"last_seen":"2025-01-12T20:19:03.629Z","linkquality":176,"local_temperature":5.5,"local_temperature_calibration":null,"occupied_heating_setpoint":8,"preset":"standby","running_mode":"heat","running_state":"heat","system_mode":"heat","update":{"installed_version":3801127,"latest_version":4063273,"state":"available"}}'
[2025-01-12 21:19:04] info:     z2m:mqtt: MQTT publish: topic 'zigbee2mqtt/bridge/response/device/ota_update/update', payload '{"data":{},"error":"Update of 'XXX' failed (Image padding contains invalid bytes)","status":"error"}'
[2025-01-12 21:19:04] error:    z2m: Update of 'XXX' failed (Image padding contains invalid bytes)
[2025-01-12 21:19:04] debug:    z2m: AssertionError [ERR_ASSERTION]: Image padding contains invalid bytes
    at validateSilabsEbl (/app/node_modules/.pnpm/[email protected]/node_modules/src/lib/ota.ts:301:19)
    at validateImageData (/app/node_modules/.pnpm/[email protected]/node_modules/src/lib/ota.ts:278:17)
    at getImage (/app/node_modules/.pnpm/[email protected]/node_modules/src/lib/ota.ts:677:5)
    at processTicksAndRejections (node:internal/process/task_queues:105:5)
    at Object.update (/app/node_modules/.pnpm/[email protected]/node_modules/src/lib/ota.ts:783:19)
    at OTAUpdate.onMQTTMessage (/app/lib/extension/otaUpdate.ts:223:41)
    at EventEmitter.wrappedCallback (/app/lib/eventBus.ts:204:17)

Looking at the image itself, it does seem to have another image (?) in an ASCII hex format (??) appended starting at offset 0x3303e. Any thoughts?