I'm having the same issue and all of my friends as well. Reboot helps but this should not be happening at all. Wrote to Bitmain. This is the response from them:

Dear XXXXXX,

Please try reloading the firmware:

https://s3.cn-north-1.amazonaws.com.cn/shop-bitmain/download/Antminer-D3-201709131713-0M.tar.gz

Run the miner for 20 minutes after loading.

If it still does not work please test each hash board separately to determine which one is defective.

To test each hash board separately: keep the PSU connectors and controller cable on one of the hash boards connected and disconnect the cables from the other two hash boards. With the miner running you can see the status of the connected hash board.

Here is more detail: http://support.bitmain.com/hc/en-us/articles/226142788-Testing-hash-board-one-by-one

On the miner status screen defective chips are displayed as "xxx", "---" or " ASIC≠72

Once you know which part is defective please create a Repair ticket and ship the part back to us according to these instructions: https://shop.bitmain.com/workOrderGuide.htm

http://support.bitmain.com/hc/en-us/articles/222648028-How-to-disassemble-miners

Please pack the hash boards carefully. If the PINs are lost due to shipping damage it will void the warranty. Here is a video demonstrating how to pack the boards: https://youtu.be/Z0LdykALhxI

Please let us know if you have additional questions or concerns.

Best regards,
Barbara
Bitmain


I haven't upgraded the firmware yet, waiting if the problem will come back.