Note that certs for an old account are still shown on the other person's page, but not on the new account if it gets recreated. e.g. at the time of writing this negative's page shows he certified salmoni, but that was before salmoni recreated his account, so his new account doesn't show that cert. Similarly, salmoni certified this account, but then it disappeared and I recreated it, so my page doesn't show the cert. God knows what that's doing to the trust metric. [Update: looks like the tmetric page crashes apache, so the answer might be that the trust metric is no longer being updated]
Possible causes could be that someone has found a way of corrupting an account by certifying it (or giving a diary rating) or that the disk is hopelessly knackered and is losing files. But I'm just guessing.