Stop resetting your spine press every single signature, try the folder trick first
Spent 3 weeks fighting a job with 40 signatures and the press kept drifting on me. Wasted so much time re-clamping after every section. Then a guy at the Chicago bindery show told me to fold each signature once with a bone folder before it goes in. Just a quick crease down the gutter. The press holds steady now for 8 to 10 signatures at a time without readjusting. Cut my run time from 6 hours down to about 90 minutes. Try a dry fold test before you touch the press next time, tell me if it holds for you too.