Thumbnail information / corrupted file?

Thumbnail is only a image of last snapshot before last save

File may be corrupted. Make a backup and open DGN with 7zip and do a verify if structure is correct. Also you could try to open file using Teigha Viewer as it is able to show missing elements. Bentley no longer provides tools for file recovery as V8 DGN is considered safe against corruption but there are still clearly some bugs how the the OLESS files are handled.

Only key-in which could help to recover file from within Microstation is "model reindex" it could recover missing models if file can be opened.

Thank you for Teigha Viewer reference - useful but I can not trace any controlable cause / solution as the file behaves unpredictably and too much conditions for here to describe. As an example just copying elements within the copy of the original file results in loosing some elements, which takes place after the reopening of the file (see illustration below). Basically I dropped this root file and redrawed everything i needed. Thanks  everyone for the responses!

Thank you for Teigha Viewer reference - useful but I can not trace any controlable cause / solution as the file behaves unpredictably and too much conditions for here to describe. As an example just copying elements within the copy of the original file results in loosing some elements, which takes place after the reopening of the file (see illustration below). Basically I dropped this root file and redrawed everything i needed. Thanks  everyone for the responses!

ahhh.. this has happened to me the culprit is usually autocad  objects converted or merged into microstation and there is some issue with the conversion .. I have found the compress with all features on and running it several times especially the options to remove shared cell definitions..

Then I make a brand new file and ref copy the compressed data dgn  into the new file  anything that doesnt come over was / is  a bad element.. and you dont want it.. most of my bad elements arent even visable but the level display tells me I have say 800 elements and cant delete the level....