What a fun film! Even from the very first teaser frame you shared, I knew this would be great.
The opening shot's oppressive, swamp-like feel is perfect, with that atmosphere carrying over into the whole short.
The CGI ghost, while totally clashing with the real Lego movements, actually benefited from that dissonance. The different movements cave it an otherworldly feel that is perfect for ghosts.

The continual technical difficulties were hilarious, relatable, and filled with all kinds of entertaining details on the error screens. Great storytelling here! The atmosphere and lighting are all top-notch, and the entire film acts as a wonderful advertisement for those "hidden side" sets. The voice acting and all the audio was great.

As for nit-picks, the camera change at 0:23 is big enough to be noticed, but small enough to feel off. While I'm sure you're aware of the 180 rule, a really quick cut away to a totally different angle would have disguised that change.  The "smear" effects, while animated very well, seemed a bit inconsistent. some movements have them, others didn't, and at 2:02 it looked like the smear went the wrong way once or twice.  Also, the "flip-phone" looks nothing like a flip phone. Great joke, though!

It's a great film, and I'm glad you shared it here!