You might be too used to DEs before going back to 1912 land. I sometimes find that it's like retraining yourself. Different shaving angles between DE/SE, for instance. I strongly suspect that if 1912s worked for you before, you'll find the groove again. They do require different handling, though: angle of use, taking your time and not too much 'buffing'.Fellow SE shavers
After a month or two away from my 1912 I have returned to it. During that time, I was using my 37c and came back to Gillette Yellow 7OCs, and got into an excellent groove.
I previously was a big fan of my 1912, but this week, I'm just finding it relatively harsh. No other major changes, ie, using my usual soaps. I can't work out why it has gone from hero to zero so dramatically. It's at the point where I am tempted to put the 1912 aside indefinitely.
Can anyone talk me out of this rut?
Don't give up. The 1912s generally are great razors and it'd be a shame to deny yourself. After all, I bet you were delighted when you first got what @Digimonkey referred to as '...a piece of shaving history.'
If you can go 2-3 days without shaving, do all the usual prep, dial in a great soap, face lather and take your time. If you use Gem PTFEs, I find they can be a wee bit harsh on the first outing. A careful hand strop can help; or even subsequent shaves may be smoother.
Hope this helps...