Bitcoin Forum

I don't think that this can happen in bitcoin, maybe altcoins but it applies to all POW(?) coins

Can you ever get a scenario where you have zero transactions to process for a block? So this is a scenario where there is no movement in the coins on the network.

The way I understand things is that there will always be at least one transaction in a block and that would be the transaction rewarding the miner for finding the block?

Sure. There have been times in Bitcoin's history, especially near the beginning where nobody has made any transactions. See the genesis block (https://blockchain.info/block/000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f) for an example.

If you mean zero transactions including no coinbase transaction, then no, I don't believe it's possible for there to be zero transactions in a block. However iirc there were stories of miners who created blocks that did not pay themselves the full coinbase reward, and were accepted by the network, so it could be possible, I'm just not sure if it has ever been done.

That's correct. The protocol rules stipulates that the coinbase transaction must always be present in the block.

In some earlier blocks, the miner had used a bad mining software which didn't claim the full amount. Reference nodes do not enforce a minimum sum of Bitcoins to be paid out, only the maximum. See: https://www.blocktrail.com/BTC/block/0000000000000000004b27f9ee7ba33d6f048f684aaeb0eea4befd80f1701126.

It seems that it is unable to decode the output address of the coinbase transaction. As a result, 12.5 BTC has become unspendable. Why was this block containing such transaction accepted by other Bitcoin nodes as valid?

Just because an explorer is unable to decode an address does not mean it is not a valid transaction. You can make all sorts of valid transactions that don't end up with a normal Bitcoin address.

The 12.5BTC isn't unspendable, its lost forever. The block reward doesn't have to be claimed. The reason why its lost isn't just because the address isn't a valid address, the value of the output is zero.