Failed to read classTweaker file from mod (Namespace Mismatch)

What it looks like in the log

java.lang.RuntimeException: Failed to read classTweaker file from mod nordic-artifacts

How to fix it

1. Find the broken mod's ID right after 'Failed to read classTweaker file from mod' in the error log.
2. Open your mods folder and check that mod's filename: if it ends with -dev.jar or -sources.jar, delete it and download the regular release JAR instead.
3. If you are developing the mod yourself, build it using './gradlew build' (which executes remapJar) instead of the plain 'jar' task, and use the output file in build/libs/ that does not have -dev in its name.
4. If you downloaded this mod from a mod site and it does not have -dev in the filename, remove the mod or install an older version, as the author accidentally uploaded an un-remapped development build.

Check your own log