When importing a DWG, some levels disappear and its elements are placed on the "Default" level
This happens when the level names include characters that are not allowed.
The characters that are not permitted in the level names include:
Ampersand ( & )Asterisk ( * )Vertical bar ( | )Backslash ( \ )Forward slash ( / )Period ( . )Less than ( < )Greater than ( > )Single quotation mark ( ' )Double quotation mark ( " )Question mark ( ? )Comma ( , )Equal ( = )
To avoid the levels being deleted during import, do the following:
That way, when importing or merging a DWG into DGN, the offending characters will be replaced with an underscore and the levels will stay in the file.
Levels And Level Libraries