Hi,
I will not answer your question fully, but I guess someone who knows can jump in.
ASDM display is based on "show vpn-sessiondb" output.
There is a chance that the counters you have are directly derived from IPsec SA liftime bytes. I.e. if liftime bytes expire, there is a phase 2 renegotiation which might cause the counters to reset.
Monitoring "show vpn-sessiondb detail remote" and "show crypto ipsec sa peer IP_ADD_RE_SS" would be a way to confirm ;-)
Marcin