Found some partial answers but my points above still stand.
1. According to various sources he was an instructor at the local club.
2. Canopy opened or partially broke off. May have triggered the parachute or made controlling difficult enough for the pilot to initiate it.
3. Try a glide with the canopy (partially) open and resulting turbulent airflow over the tail.
Good luck.
Source:
https://aviation-safety.net/wikibase/280419