5th gear lock out?

So this is weird, but this has happened to me the second time this morning on the way to work. Whats happening is that just casually driving, after rowing through the gears, 5th gear seems to be locking out while moving. Letting the clutch out in neutral, trying to rev match, nothing. All the other gears, no problem. Happened to me the other day. I come to a stop and pull over, and then am able to row through all the gears while stopped. Same thing this morning. Checked the shifter linkage, Diesel Geek Sigma shifter, solid shifter bushing, and end links. Everything seems fine, no sticking. After pulling off, everything was once again normal. About 1 week ago, I flushed the brakes and slave with Motul 600, car felt great after, as well as the gear box oil was changed to Motul 300w as recommended. Again, gear box felt substantially better after the gear oil change. Shifts are so smooth and crisp. I did have a track even last Saturday, but only stayed in 3rd the entire length of the track. Afterwards, the gear box didn't shift any different. Even after this lockout happens and I come to complete stop, everything is fine afterwards.

Anyone else have a similar situation with 5th gear locking out? I searched and it seems that the 6spd guys had similar issues.

So there were 2 days this past week were it was completely locked out of gear regardless of what I tried, even with the car off.

Went to re-align my shifter and noticed the neutral lock pin on the shifter turret was wasn't doing a damn thing. Took the shifter turret out, turned upside and a small broken pin fell out. I must've broken it while having it engaged when torqueing down the nut on the shifter assembly, and it was jamming the shifter from pulling up into fifth gear. I will continue to monitor this. It shifts fine, as it did before, but no more episodes.