Both CuraLE 2.6.69 and 3.2.19 fail to load ASCII .stl files. Cura 3.3.1 loads them without issue. Convert the files to binary .stl files and they will load. Multiple tools can be used to do the conversion, Microsoft's 3D Builder, Meshmixer are two.
This failure was reported in https://forum.lulzbot.com/viewforum.php?f=8&sid=bde2bc2db128432252a277a31b509e5a
I have attached the ASCII .stl files.