Error when trying to set an association group on Z-Wave dimmer

I am trying to set an association group on a particular ZW500D dimmer (not a ZW500DM).
I am able to do it on other dimmers without issue. However when trying to do it with that one, I see in the log the following error:

2017-10-17 17:54:04.952 [ERROR] [ome.io.rest.core.thing.ThingResource] - Exception during HTTP PUT request for update config at ‘things/zwave:device:XXXXXXXX:node16/config’ for thing ‘zwave:device:XXXXXXX:node16’: null

What could be causing such a problem with just this one dimmer?

PS: It is actually not the only dimmer that has this issue. One different model has the same issue. However two other dimmers of this type and one of the second type have no issue.

Which version of the zwave binding? This error has been reported recently by others in the dev binding thread:

Version 2.1.0.
I even tried to unpair the dimmer, re-pair it (which gives it a different node number) and the same thing happens.

More information. In the userdata/jsondb/org.eclipse.smarthome.core.thing.Thing.json file, the working device and the non working device have entries that are identical, except for the node number and the label until it gets to the section configuration. The one that does not work only has:

“configuration”: {
“properties”: {
“config_1_1”: 0,
“switchall_mode”: 255,
“config_2_1”: 0
}
},

The working one has many lines that seem to be related to associations:

“configuration”: {
“properties”: {
“group_org.openhab.binding.zwave.internal.protocol.ZWaveAssociationGroup@XXXXXXX”: [
“node_1_0”
],
“group_org.openhab.binding.zwave.internal.protocol.ZWaveAssociationGroup@YYYYYYY”: [
“node_1_0”
],

Also when removing all the items, removing the thing and then trying to put them back, the console gives another message. This time a warning:

2017-10-17 22:27:28.259 [WARN ] [ome.core.thing.internal.ThingManager] - Initializing handler for thing ‘zwave:device:XXXXXX:node69’ takes more than 5000ms.

The plot thickens.
I thought I’d try setting the association with a different software. So I ran open-zwave-control-panel
When I try to set the association group, I get:

2017-10-18 10:54:45.154 Info, Node069, Association::Set - Adding node 15 to group 1 of node 69
2017-10-18 10:54:45.154 Detail, Node069, Queuing (Send) AssociationCmd_Set (Node=69): 0x01, 0x0b, 0x00, 0x13, 0x45, 0x04, 0x85, 0x01, 0x01, 0x0f, 0x25, 0xa3, 0xaa
2017-10-18 10:54:45.154 Info, Node069, Get Associations for group 1 of node 69
2017-10-18 10:54:45.154 Detail, Node069, Queuing (Send) AssociationCmd_Get (Node=69): 0x01, 0x0a, 0x00, 0x13, 0x45, 0x03, 0x85, 0x02, 0x01, 0x25, 0xa4, 0xa7
post: key=groups data= size=0
2017-10-18 10:54:45.154 Detail,
2017-10-18 10:54:45.154 Info, Node069, Sending (Send) message (Callback ID=0xa3, Expected Reply=0x13) - AssociationCmd_Set (Node=69): 0x01, 0x0b, 0x00, 0x13, 0x45, 0x04, 0x85, 0x01, 0x01, 0x0f, 0x25, 0xa3, 0xaa
2017-10-18 10:54:45.162 Detail, Node069, Received: 0x01, 0x04, 0x01, 0x13, 0x01, 0xe8
2017-10-18 10:54:45.162 Detail, Node069, ZW_SEND_DATA delivered to Z-Wave stack
2017-10-18 10:54:45.212 Detail, Node069, Received: 0x01, 0x07, 0x00, 0x13, 0xa3, 0x00, 0x00, 0x06, 0x4e
2017-10-18 10:54:45.212 Detail, Node069, ZW_SEND_DATA Request with callback ID 0xa3 received (expected 0xa3)
2017-10-18 10:54:45.212 Info, Node069, Request RTT 57 Average Request RTT 58
2017-10-18 10:54:45.212 Detail, Expected callbackId was received
2017-10-18 10:54:45.212 Detail, Expected reply was received
2017-10-18 10:54:45.212 Detail, Message transaction complete
2017-10-18 10:54:45.212 Detail,
2017-10-18 10:54:45.212 Detail, Node069, Removing current message
2017-10-18 10:54:45.212 Detail,
2017-10-18 10:54:45.212 Info, Node069, Sending (Send) message (Callback ID=0xa4, Expected Reply=0x04) - AssociationCmd_Get (Node=69): 0x01, 0x0a, 0x00, 0x13, 0x45, 0x03, 0x85, 0x02, 0x01, 0x25, 0xa4, 0xa7
2017-10-18 10:54:45.220 Detail, Node069, Received: 0x01, 0x04, 0x01, 0x13, 0x01, 0xe8
2017-10-18 10:54:45.220 Detail, Node069, ZW_SEND_DATA delivered to Z-Wave stack
2017-10-18 10:54:45.273 Detail, Node069, Received: 0x01, 0x07, 0x00, 0x13, 0xa4, 0x00, 0x00, 0x06, 0x49
2017-10-18 10:54:45.273 Detail, Node069, ZW_SEND_DATA Request with callback ID 0xa4 received (expected 0xa4)
2017-10-18 10:54:45.273 Info, Node069, Request RTT 60 Average Request RTT 59
2017-10-18 10:54:45.273 Detail, Expected callbackId was received
2017-10-18 10:54:55.215 Error, Node069, ERROR: Dropping command, expected response not received after 1 attempt(s)
2017-10-18 10:54:55.215 Detail, Node069, Removing current message
2017-10-18 10:54:55.215 Detail, Node069, Notification: Notification - TimeOut
2017-10-18 10:54:55.215 Info, Notification: Notification home e551caa9 node 69 Timeout

So it does seem that the issue is on the device side, not on the openHAB side. Either it is defective, or there’s another setting that needs to be changed before its association can be changed. The only thing that is a bit funny now is that when trying to change the association, openHAB gives an HTTP error immediately, not after a timeout like open-zwave. But that could be due to earlier timeout message when openHAB start that maybe marks the node as not responding?

@chris Do you have any idea? You’re the specialist of Z-Wave.

New discovery: This particular dimmer has a different firmware version from all the other: 2.2 while the others have version 1.4. All the others can be put into an association group. This is the only one refusing to join of all my ZW500D dimmers.
Some other dimmers are also not allowing me to set the association groups. Their type is: WD500Z-1 running Firmware 5.41.