After the Lightroom 7.3 update, .SRW files from Samsung NX cameras are filtered out when trying to import from an SD card. Only JPEG and other types are shown. The issue appears if the SD card is selected as the Source under the Devices section. The files show up normally if the SD card is selected under the Files section.
Also. If the SD card is inserted after Lightroom is opened, then the .SRW files show up everywhere as well.
It appears to be a bug with the .SRW extension, because you can take any RAW file that Lightroom would normally detect in the import dialogue and rename its extension to .SRW and then it won't be detected, unless I do the workarounds I mentioned.
In LR versions 7.2 and before, the issue isn't apparent and the .SRW files are detected in all situations.