It's just a commonality with these transmissions. You can literally feel the transmission clunk into first through the clutch pedal when you finally get it into first after the "lock out". It's not a lock out, it's just the transmission locking us out from 1st. Mine only does it while cold, and sometimes I have experienced the stationary lock out, normally it's only while moving though.
I just take it easy while cold because you can feel how unhappy the transmission is to go into first at times and I'm not going to force it. It's an common issue, anyone else I've talked to with an Si has this issue.
I had it happen once after putting the Acuity bushings in. No big deal, go to second, then back to first. Happens once in a great while with most MT's. This spring I'll check the clutch adjustment just to eliminate that. When It's out of warranty. I'll try synthetic gear lube and hope I don't get seepage.
This happens to me sometimes, not that often though at a dead stop. I just throw it into 2nd gear and back into 1st, and it slides in like butter. Also if I am going around 15KMPH (10MPH) in 2nd gear or neutral it locks me out of 1st gear.
I usually get locked out once out in first gear once or twice a day. Im gonna change to amsoil fluid now and see how it does. I also have a few acuity upgrades. While that helped with smoother shifting im still getting that lock out.
Every manual I have ever driven, from a VW GTI to a Toyota Corolla experiences this issue occasionally. Especially when cold. If you release the clutch and push it back in, the car will go into gear. A real lockout is when you always have a hard time getting it into gear or cannot get it to gear without using force. Back in the day I had an 86 GTI, I was showing off to my GF and broke the rear engine mount. I didn't have the money to replace it and gear after gear (starting with R) started to lock out. Eventually it was not drive-able anymore, and that was that!