Hi, Thanks mercedes508 for reporting this issue with seahorse. However, it appears that the error you face "trying for the first time to sign, every signature after that first error goes fine." is not related to the one that was tracked by this bug.
I thus cloned this bug report as 862552 [1]. Please follow up there. Thanks again for your contribution! 1: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=862552
