zPools (Mike) and Burster51 (our new community coin developer) have been working on the new masternode reward system.

It is now improved to what we call "SONO fair masternode reward lottery system". The winning masternode is randomly selected based on a lottery ticket . Each masternode gets a new lottery ticket number with every SONO POW/POS block.

It is possible to see the lottery ticket number on the command line ./SONOd masternode list rank or on the GUI wallet. If you look at that please be aware that this is the lottery ticket number and does not mean a ranking order or when you can expect a reward for your masternode.

The masternode winning the reward is selected randomly by fair lottery. The wallet update is not mandatory, but if you please update at your earliest convenience that will be fantastic. The more nodes that run the "SONO fair masternode reward lottery system" the better for the fair distribution of MN rewards to everybody.
And just a remark on that specifically - if you browse masternode statistics on the official block explorer here, you will notice that on some days some of the masternodes receive double digit rewards say between 20-50.

This is completely normal and intended.
Whenever a person holding about 1000 SONO in a cold wallet (offline) or locked in a masternode for several months and decides to stake those coins there will be substantial reward for that stake. Which is completely fair too because the coins had been locked or cold for a long time.

You can download the new wallets here: https://github.com/zPools/sonoa/releases

The official Change log:

-     Masternode Reward system changed to "hash-distance-distribution".
Our new Masternode payments are based on the hash distance. This hash is calculated with the Blake algorithm. Blake is a fast and secure algorithm that will work very well for this task. This algorithm is only used for calculation the hash for the hash distance distribution and its not used anywhere else.

-    New seed is available and coded into the wallet to make it easier for new wallets to get onto the network and synchronize faster.  

-    The auto generated "sono.conf" is now a bit smoother to work with.  

-    When you compile the wallet yourself, you will now get a lot less warnings making it easier and faster to compile.

-    Minor changes to the code, which makes mandatory updates easier to work with.  

-    We cleaned the repository and removed many outdated and insignificant files.  

-    We added a dependency script for Ubuntu 16.04. We forked it from Lux and made it fit for SONO