If you have been staking for more than a few weeks you have probably had an orphaned staking reward transaction. These typically show in your wallet with [brackets] around them and are not added to your wallet balance. If you look in the transaction tab in your wallet there will be some kind of indication on the left hand side with a short explanation. In the example below, the question mark indicates there was an issue completing the staking transaction, and the explanation says, ‘Generated but not accepted Mined.’
I will refer back to this picture again in the explanation below.
The two main factors I have seen causing orphaned blocks are being on the wrong fork of the coin you are staking, or someone else completing the staking process more quickly than you. I also have found an explanation stating if you are staking with the same wallet on more than one computer you are likely to see orphaned rewards.
If you are on the wrong fork it will be obvious. You will start receiving many orphans back to back. The fix for this is easy. There is probably a new wallet you need to upgrade to, or you may just need to sync the blockchain again from scratch. Check in the chat room (slack/discord) of the coin to see if there is an updated wallet.
All is not lost if you receive a random orphaned staking reward. There are two types of Staking rewards. Each digital currency reward will either be a fixed amount or a fixed percentage.
PIVX is an example of a fixed reward. Each time you successfully stake you receive 2.1599896 PIVX (currently) as a reward. In my PIVX wallet when I have an orphaned transaction it is typically for a reward different than 2.1599896 PIVX. Approximately 75% of the time, I have received a successful reward following an unsuccessful orphan. As shown in the screen shot below, the orphaned transaction was for the incorrect amount, followed by a successful reward. Check your staking transactions in your wallet to see if this is the case for you. If so, it can help alleviate some of that irritation you have been experiencing when you see the orphans show up.
The first screen shot (near the top) was from a currency called OP Coin (OPC). It rewards a fixed percentage which can fluctuate based on how long it takes to receive a staking reward. For example, if it takes 48 hours to stake you will receive twice the reward you would have received if it had taken 24 hours. The orphaned rewards in this type of wallet usually continue staking. If you look at the screen shot you can see the reward for 4320 OPC did not complete, but 32 hours later a successful staking transaction rewarded more (5196) coins for the same address. The reward continued to accumulate even though there was an unsuccessful orphaned reward. This happened approximately 80% of the time in my wallet.
Orphaned rewards can be frustrating, but as you can see in the two examples above, they are not always as bad as they seem. Often you will make up for the missing coins within the next few hours, or with your next successful stake. Check the transactions in your wallet and see if this has been the case for you also.