After some problems with forks for a while and after upgrading my wallet to the latest version (3.7.7.0) it seems that my ballance is only less than half than it was before. I also used the Advanced -> Download Blocks menu item to rebuild my local blockchain.
The wallet now seems to be fully synched but shows only around 19k GRC:
But before I had around 44k GRC and according to gridcoinstats.eu my balance is still correct.
Maybe it has something to do with a part of my balance is still on stake?
Has anyone any hints on how to fix this?