Adding older ZigBee (Adhoco) devices


I’m a ZigBee2MQTT newbie.

I own an older, proprietary HA system based on ZigBee protocol. I bought it in 2011.
The company, Adhoco, went bankrupt a couple years later. This means I can’t get spare parts, devices to expand the system, software updates and, since the coordinator / automation server was accessible only via a cloud service, have no access to the system anymore. It ran fine until lately. Now I have issues that can’t be solved anymore.
The brand is still there, but nothing/nobody that could solve my issues. No documentation at all available.

My idea was to get rid of the “proprietary” handcuffs, replace the existing coordinator / automation server with openHAB and continue using all the ZigBee actors, sensors and switches I have. That would save me quite a bit of money. Replacing faulty devices or expansions would be done by new devices of any brand.

I have an openHABian server and ZigBee2MQTT with a cc2531 coordinator running but I can’t pair the old ZigBee devices.
I always end up with the error
info 2020-03-14 16:29:59: Starting interview of ‘0x0018e50000002800’
info 2020-03-14 16:29:59: MQTT publish: topic ‘zigbee2mqtt/bridge/log’, payload ‘{“type”:“pairing”,“message”:“interview_started”,“meta”:{“friendly_name”:“0x0018e50000002800”}}’
error 2020-03-14 16:30:59: Failed to interview ‘0x0018e50000002800’, device has not successfully been paired
info 2020-03-14 16:30:59: MQTT publish: topic ‘zigbee2mqtt/bridge/log’, payload ‘{“type”:“pairing”,“message”:“interview_failed”,“meta”:{“friendly_name”:“0x0018e50000002800”}}’

and database entries like:

I can sniff the traffic. The old devices and the new cc2531 are in some way talking to each other, but don’t seem to understand each other.

After I invested quite some time in troubleshooting I got doubts if what I’m trying to do is possible at all.

So my question, can anyone tell me if it is possible at all to somehow integrate 2011 devices in a 2020 cc2531/ZigBee2MQTT/openHAB environment or is it just a waste of time trying?