Don't quote me on this because it's a very hazy recollection, but I think I recall a situation where PCR for VBR-nrt was slightly under configured by the provider, which caused some cells to be dropped. When the receiving SAR tried to reassemble the IP packet it recorded a hit against CRC for the packet. The insidious issue was this was only seen under full load when the incorrect PCR was occasionally exceeded. Again, can't say it's related to your issue but if using something like VBR, insure PCR is properly configured both on ATM routers and by the ATM provider.
