Also try the command-line version by prefixing the purge command with a minus sign. Then purge RegApps, Empty Text & Zero Length objects. Then do a regular purge again (including blocks, layers, styles, ltypes, dimstyles, etc.) - do this at least 3 times as there may be nested stuff. Also check if there's a huge amount of layer-filters / and/or states.
Check if there's any blocks left in the drawing (use the Insert command). If there are, then they must be inserted somewhere on something like an Off/Frozen layer or on a different layout. Zoom Extents after turning on all layers on each layout to make sure there's not something hiding several miles off to a side.
If still there's a problem, start the MOVE command and then type ALL when asked to select objects. See what's displayed on the command-line.