What I tried so far:
- clear caches (CWM)
- reflashed cm11
- format sd card in windows (fat32)
- format sd card in windows (ext4)
- format sd card in CWM (failed)
- mount sd card in CWM (failed)
sd card is working in card reader (both win/linux) and worked before in stock ROM, so I assume it is not broken and generally compatible to the phone.
any suggestions what else to try?