Heat and Glass
If you are firing Spectrum S96, even at 677C you are not really getting a proper tack fuse with only 30mins at the temperature. The bumps and indentations are probably a result of an incomplete adhesion of the glasses. Tack fuses normally occur in the 720-760C range.
Don’t rely on the pre-programmed schedules. Instead look at some of Paul’s here on the site.