support line, abutment, pier, beam layouts gone from Explorer interface in OB

I had a 4 span bridge model set up in OB, (OBD CE 2021 Release 2) all looked as it should and all of it appeared in the Explorer drop down.  

I found though that bridge item levels had not been assigned correctly, many Decor items as well as some 3d components were on the level "default".  

I reassigned linework to named levels, and things started disappearing (trying to be careful to assign linework bits, not the whole element/object).   

First a Support Line was gone, I had turned off the supportline level to access other items and when I turned it back on, supportline 4 out of 5 was gone visually and from the Explorer. 

Then, awhile later, the End Abutment (associated with supportline5), which is a parametric cell that had been listed as a "special pier" in the Explorer, was still in drawing, but gone from the Explorer list.  It could still be tagged and showed up in Properties as it had been in Explorer, something like: Support-Pier-Special pier.

Then the Beam layouts for spans 3 and 4 would not turn on, the beams are still there, and the layouts were still listed but with unchecked boxes, if try to check it results in endless "please wait..." box.

Then, hours after the supoportline4 vanished, Pier 3, associated with the originally disappeared support line 4, was gone from the Explorer list, still visible in the drawing, but when tagged a warning box says "object not set to an instant of an object."    

Then supportline 5 left the Explorer, though still visible and tagable like the End Abutment.  

So now only have Supportlines 1,2,3, the Start Abutment and Piers 1 & 2 as support components in the Explorer.

This didn't happen all at once but over an 8 hour day.  (with reloadings and rebootings in between, thinking at first it was something our guru could restore, but it baffles him also)

I'm going to have the OB model dgn restored to where it was a few days ago, but that will leave me with useless levels again.

If I accidentally erased Supportline 4, why did it take so long to affect other components?   

Why weren't the items assigned levels they normally are?