I had a very similar issue where the dhcp snooping database had stopped updating. I could watch the write delay tick down, and at 0 nothing would happen. Not success or failure counters increment, just nothing, but the write timer would reset and start counting down again. The last successful dhcp write time, however, corresponded to an NTP ACL change that had been made (which disrupted ntp sync on the switch). The clock was write, just not ntp sync'd. After investigating and correcting the ACL, and getting NTP synced again, the dhcp writes started working again. I'm not sure of the correlation, but it may be worth looking at, if you're seeing dhcp database write errors (local file or url).
