After a full day at Hallett, my car wouldn’t go into gear and I had to have it towed back home to Dallas from Tulsa (thanks for the help @Spaceman Spiff). I incurred a rather painful towing fee even with AAA membership.
About 5,000 miles ago, I replaced the factory clutch, pressure plate, throwout bearing, flywheel, and pilot bearing (all with the Flyin’ Miata Happy Meal Kit). The service went smoothly for the most part, except I had a difficult time mating the transmission to the engine. I wrestled with it for a while before I grew frustrated and jammed it in a bit roughly and buttoned everything back up. The car ran fine with no suspicious noises until it wouldn't go into gear a few weeks ago at Hallett.
My observations upon dropping the transmission:
The throwout bearing is clearly not centering on the pressure plate diaphragm/fingers (see Exhibit A below).
The pilot bearing is severely damaged with about half its roller bearings missing/torn off (see Exhibit B below).
I believe I may have screwed something up when I impatiently strong-armed the transmission while mating it to the engine. The clutch may have not been perfectly centered (even though I used the alignment tool) which made the transmission/engine mating more difficult. This may have caused the TOB to be off-center on the pressure plate diaphragm and eventually led to the pilot bearing failure.
I have little experience with this sort of thing, so I'm hoping someone here can confirm or deny my diagnosis.
Exhibit A - throwout bearing not centering on pressure plate
Exhibit B - pilot bearing failure