Hi, may I ask a naive question?

I noticed that once a while there are couple of blocks with 22.66 block rewards instead of 25, for example:

https://chainz.cryptoid.info/ric/block.dws?7d613e7cb67c960620d11c8cc5d958cad179bce7480322e3de4939ef501e3374.htm

Do you know what is the cause? Is that a mining software bug or something in the Riecoin consensus rules?

Thanks!