Split kohlrabi

I've had a couple of very good crops of kohlrabit this year, but when I was picking them today I noticed two of them had split (in the bulb/swelling), and one of them had started to go soft and mushy in the split. Is this likely to be a watering issue or slugs? The rest of them are all fine, it's just the last two in the row.

I'll drink to that Yorkie. 

Cheers,    Tony.