When the Warnings Plug-in parses a JCReport file, it expects the severity levels to be capitalized, like "Error" or "Warning": https://github.com/jenkinsci/warnings-plugin/blob/warnings-4.64/src/main/java/hudson/plugins/warnings/parser/jcreport/JcReportParser.java#L83

However, JCReport itself appears to use lower-case severity levels "error" and "warning": https://github.com/jCoderZ/fawkez-code-report/blob/5624ac77dcd11067f27b001bcb1ee3f1c06076e2/fawkez-code-report-core-base/src/main/java/org/jcoderz/phoenix/report/Severity.java and https://github.com/jCoderZ/fawkez-code-report/blob/5624ac77dcd11067f27b001bcb1ee3f1c06076e2/fawkez-code-report-core/src/main/resources/xjc/report-types.xsd

I have not tested the behavior of JCReport in practice.

Split from JENKINS-48669.