Here are two screenshots, "before" from the file I uploaded to BIMx before the glitch, "after" from the current state of the AC file -- floor is gone, wall and structure gone, stair stringers gone, half the stair tread standoffs gone, several glass floor panels gone including one's SEO effects on the upper floor.
None of what's missing in the current model gives any clue as to why. It's not group related, layer related, structure related, renovation related, element related, object related, location related, not 3D filtered, not 3D cutaway, not anything I can think of.
And now the welder is on site and the contractor is asking for a steel detail revision for the stair stringer brackets which are no longer in my model! Aaaaaaahhh!
AC fan since v 7. Currently on AC 26 Build 5003 USA FULL Apple Silicon,. 2022 Mac Studio, 32G ram. OS X 12.6.2