There's a new mandatory, 5.3.0.0.
It fixes a bug in the 5.2.0.0, 5.2.1.0, and 5.2.2.0 releases where the new solo cruncher fix doesn't work correctly on some wallets. Most new solo crunchers are fine, but (currently) three solo crunchers are affected. The issue is that most 5.2 wallets get it correct for all, but some don't.
If any of those affected solo crunchers stake, it will cause forks for 5.2 wallets because of this. If you don't upgrade, you can potentially fork in the future. There is no hardfork block to upgrade by due to the nature of the problem, so upgrade immediately
For more information see the post from Jim Owens on Reddit about the release