Yz250 false neutral

I was racing today (woods racing) and in a field section I went to shift up and hit a false neutral. I shifted down and it was kind of hard to shift down. Well I was nervous about it so I left it in 3rd for as long as I could until I had to switch again. Once I switched again everything felt fine. I finished the race and went through all the gears and it has not done it again. Bottom end was rebuilt 21 hours ago and I looked over the transmission but no wear. Whenever I rebuilt it I had an issue with the 5th gear fork not transferring over to the opposing case because of a burr that was in the way. Once I removed the burr it shifted fine. Now this. What should I look for? I would like to not split the cases but obviously I will if I need to. Could this be from the shift paws being wore? I have read that. Also, it seems as though my shift shaft has a little more play than usual between shifts. Probably 1/2 an inch or so. Makes you think the shifter is loose but it’s not. Another thing, my basket has started to get grooves in it. Very small but it needs to be replaced. Could the false neutral be caused by the clutch slipping or something?