Checkstyle plugin throws error when UnusedLambdaParameterShouldBeUnnamed is configured

[FelixStumvollDT]

When configuring the UnusedLambdaParameterShouldBeUnnamed check, the plugin throws the following error:

The Checkstyle rules file could not be parsed.
cannot initialize module TreeWalker - cannot initialize module UnusedLambdaParameterShouldBeUnnamed - Unable to instantiate 'UnusedLambdaParameterShouldBeUnnamed' class, it is also not possible to instantiate it as .UnusedLambdaParameterShouldBeUnnamed, UnusedLambdaParameterShouldBeUnnamedCheck, .UnusedLambdaParameterShouldBeUnnamedCheck. Please recheck that class name is specified as canonical name or read how to configure short name usage https://checkstyle.org/config.html#Packages. Please also recheck that provided ClassLoader to Checker is configured correctly.
The file has been blocked for 60s

The same can be observed for the UnusedCatchParameterShouldBeUnnamed check.
Both checks work when executing checkstyle via gradle

Plugin Version: 5.114.0
Checkstyle version configured in Gradle: 12.1.1
IntelliJ Version: 2025.2.4
JDK Version: 25

[jshiell]

Could you please attach your rules file?

[jshiell]

Also, when you say JDK version - is that the project JDK, the IDEA JDK, ... ?