LibravatarService.FromEmail missing '@'

Every day I can see a error message in log:
ls/avatars/avatar.go:117:LibravatarURL() [E] LibravatarService.FromEmail(email=lucas.ribeiro): error mail: missing ‘@’ or angle-addr

So a tried veirfy the user data, but I can not found wrong information.
I looked at table “user”, verified the fieds: email, avatar_email and bolth is ok.

I found a table email_hash contains a line with “lucas.ribeiro”, so I deleted it, and the next day the line is there again.
How this table (email_hash) is populed, where is source data ?