Air Carrier Pilot reported a large pitch down moment; resulting in an autopilot disconnect and sink rate warning when on final approach. The flight continued the approach and landed safely.

Narrative

This is a follow up from a report I submitted several months ago. Essentially; the aircraft experienced a large pitch down moment while capturing the glide slope on ILSZ runway R RNO that resulted in the autopilot disconnecting and a sink rate" callout. I am following up because I was recently jumpseating on an air carrier into RNO and it came to my attention that this is a known anomaly for this approach that is included in their company notes. Perhaps this should be included in our company notes as well. On ILSZ approach runway 17R into RNO. Autopilot and autothrottle were engaged and aircraft was in LNAV VNAV in VFR conditions with the speed window closed. After ATC approach clearance; I armed APP mode once established inbound on the final approach course after the fix WALAR. We configured early to achieve stabilized approach criteria. The gear was down with flaps 15 just prior to DISCS. The aircraft leveled off at 7;400 momentarily before G/S mode engaged at DISCS and the aircraft captured the glide slope. Because of high terrain in the area; the 2;500 ft RA callout had already been made with the appropriate altimeter setting callout. With the autopilot engaged; the airplane dove to catch the glide slope resulting in one "sink rate" callout. The autopilot also disengaged; either in its own or because of the forces placed on the control column by myself as pilot flying upon hearing the sink rate callout. No autopilot disengage button was intentionally pushed. The autopilot remained off for the duration of the flight and the rest of the flight was conducted uneventfully. It should be noted that thermals were present at the time of the event."