Using the wrong chain after a fork
How a fork works
When a blockchain hardforks, a new version of the blockchain is created while the old is left behind. This typically happens at a certain block height.
When Sia forked, it occurred at block 179,000 and means that we now have a new chain that the Sia team will be supporting. There's also the non-fork chain that can either be maintained by a separate group, or forked again to create a new project. Here's a visual representation of the recent Sia fork.
What this means for users
Frequently, after a fork, users of a blockchain don't update right away. This means that while the main network is operating on
version Y, some users are operating on
version X. If you're on
version X and try to send coins to an address that's using
version Y, they won't go through.
The same is true for Sia. If you have not updated to 1.3.7 or later, but send coins to someone who has updated, the transaction won't be received on the other end. It will look like those coins have disappeared.
Since all exchanges that trade Siacoin have updated to 1.3.7 or later, sending coins to an exchange from a pre-1.3.7 wallet will result in the loss of those coins.
Your coins are safe
You have not lost your coins. At least, not your main network Siacoins. Since you were on the old chain when you sent them to a 1.3.7 wallet, you sent and lost your old chain coins – the coins that would have been spendable on forks of Sia.
Once you update to 1.3.7 or later, your coins will reappear. Any coins held in your official Sia wallet as of block 178,999, just before the hardfork, will be accessible in your wallet once you update Sia and sync the new version of the blockchain.
Now that you're updated, to sync the new version of the Sia blockchain you first need to delete the old one. Quit Sia.
If you're on 1.3.7, you can easily find these folders by clicking Show Sia Data in the About tab.
If you're on 1.4.0 or later, use the Info button at the top of Sia.
Then click Show Sia Data.
Once you find the /sia folder:
transactionpool folders. Reopen Sia to let it sync the correct version of the blockchain.
Special considerations for miners
Miners might be affected in other ways by a fork. If you've set up your miner to mine a certain coin, a fork might change the algorithm associated with mining that coin. An example of this was the recent Sia network hardfork, which invalidated all ASIC Sia miners except those produced by Obelisk. If you were using a Bitmain A3, Innosilicon S11, or any other non-Obelisk ASIC miner, you were no longer mining the primary dev-supported Sia chain after the fork.
What this means for you is that your miner has still been working, but it has been mining the pre-fork version of Siacoin which is going by some different names, one of which is Siacoin Classic. These coins that are mined will not be visible in your wallet once upgraded to 1.3.7 or later.
Any coins you had mined prior to the fork will be visible in your wallet once you upgrade to 1.3.7 or later.
You’ll want to research the forks of Siacoin and see if there is any development on those fronts, and if they are tradable on any exchanges. Unfortunately, since our team only develops and supports one instance of Siacoin, this is the only bit of info we don’t have readily available.