So occasionally, I miss a shift

, and afterwards 1st and reverse are hard to engage. It happened again on Monday.
For the first mile afterwards, it wouldn't even try to go into first. The shifter just felt bound up. Gears 2-5 were OK.
After that, it would partially slip in (

), but would pop right out it I tried to give any throttle.
I left it parked for ~5 hours at work, then went to head home. At first it was still a little tough to get into first, but it felt like it went in fully (

). Fed in a little power and it stayed in gear fine. It felt like it was getting easier each time I put it into first.
Yesterday and today it pretty much feels fine.
This isn't the first time it's behaved like this either. Once after a missed shift at the track, and once more on the street.
Anyone else had a similar problem? Any insight as to what might be the issue? I did drain and fill with fresh Extra-S, but it's happened both before and after that service. Is it just a matter of time before my tranny goes?