I have a 98 Stagea (all of 3 weeks) with an RB25DE (Neo) motor that was showing similar if not identical symptoms.
In my case the motor would fire up fine when cold, however if the motor was hot eg 5 minute run or longer it would spin freely for a few seconds, then suddenly almost completely seize up, as in the starter sounded as if the battery had suddenly died. - Leave the bonnet open for 5 to 10 minutes and it would start reasonably normally.
(Battery new! everything else about the vehicle mint or near mint)
The answer was the Crank Angle Sensor mounted on the end of the exhaust cam was all chewed up.
Seems some Dick Head 'Professional' mechanic at a local garage had not put it back on properly when the Cam Belt was changed 2 years ago. The slotted disk had been slowly chewing through the LED Sensor ever since.
'My' Professionals tried to find a second hand one without success, so they had a go at Repairing it. I've only just got the car back tonight and they are saying to see how it goes. Methinks I'll be on the lookout for a new/used 'unchewed one, even though it appears to be starting just fine now.
BTW it took 2 years to get to the critical stage because the previous owner (very fussy careful owner I might add) only did 3000 Km in that time.
Paul.
PS (next day)
My garage guys rang to say one of their contacts had found a used CAS and sent it overnight, would I like it installed, you bet. Took literally all of 5 minutes to install.
I don't know if I'm imagining it but it seems to both start and run much sweeter now.
I've also found out that the original botched job was 20 months ago and the car had only travelled '1700' Km since, 1000 KM of which I had done.
Cheers
Paul.