No problem for me with 2.1.2 on Ubuntu 18.04 (Puppy Linux derivative).
"RS_FilterDXF::addLayer: layer 0 have extended data
RS_FilterDXF::addLayer: layer 0 is construction layer" - Layer 0 set as construction layer? If so try switching off.
File of foreign origin? Or contains elements of foreign origin?
Has been opened and saved again in different CAD?
Zooming in and out too furiously? Might confuse and lock up LC.
Maybe the reason is outside of LC.