When is "type":"DEVICE_QUEUE_ITEM_FCNT", "error":"invalid frame-couter" occurred?

Hi,

I’m using MQTT interface to send multiple downlink frames.

My case is below.

I published /tx topic to send 3 downlink frames.
The first frame was sent. But there was no ack, so I received /ack topic message with "acknowledged":false.
Then I received /error toplic messages with "type":"DEVICE_QUEUE_ITEM_FCNT", "error":"invalid frame-couter" about next two downlink pending frames.

Is it a correct case?

I’m using LoRa App Server 1.0.1 and LoRa Server 1.0.0.

I made a pull-request about it.
Please, check it.

I think this was already fixed in LoRa App Server v1.0.2

v1.0.2
Bugfixes
Lock device row on downlink enqueue to avoid duplicated frame-counter values (#245)