Jobs are missing from UI. When checking on Jenkins Home directory all the required build folders and config.xml are present. After comparing config.xml from old config.xml file found that the tags for plugins and class are missing.

Found below on logs.

Caused: java.io.IOException: Unable to read /var/lib/jenkins/jobs/{JobName}/config.xml
2020-08-18 06:43:44.972+0000 [id=57] WARNING c.c.h.p.folder.AbstractFolder#loadChildren: could not load /var/lib/jenkins/jobs/{JobName}
org.xmlpull.v1.XmlPullParserException: name expected (position:START_TAG <org.jenkinsci.plugins.pipeline.modeldefinition.actions.DeclarativeJobPropertyTrackerAction>@5:97 in java.io.InputStreamReader@3a530a3f)
at org.kxml2.io.KXmlParser.exception(Unknown Source)
at org.kxml2.io.KXmlParser.error(Unknown Source)
at org.kxml2.io.KXmlParser.readName(Unknown Source)
at org.kxml2.io.KXmlParser.parseStartTag(Unknown Source)
at org.kxml2.io.KXmlParser.nextImpl(Unknown Source)
at org.kxml2.io.KXmlParser.next(Unknown Source)
at com.thoughtworks.xstream.io.xml.XppReader.pullNextEvent(XppReader.java:109)
Caused: com.thoughtworks.xstream.io.StreamException: : name expected (position:START_TAG <org.jenkinsci.plugins.pipeline.modeldefinition.actions.DeclarativeJobPropertyTrackerAction>@5:97 in java.io.InputStreamReader@3a530a3f)
at com.thoughtworks.xstream.io.xml.XppReader.pullNextEvent(XppReader.java:124)
at com.thoughtworks.xstream.io.xml.AbstractPullReader.readRealEvent(AbstractPullReader.java:148)
at com.thoughtworks.xstream.io.xml.AbstractPullReader.readEvent(AbstractPullReader.java:135)
at com.thoughtworks.xstream.io.xml.AbstractPullReader.move(AbstractPullReader.java:118)
at com.thoughtworks.xstream.io.xml.AbstractPullReader.moveUp(AbstractPullReader.java:113)
at com.thoughtworks.xstream.io.ReaderWrapper.moveUp(ReaderWrapper.java:40)
at com.thoughtworks.xstream.io.path.PathTrackingReader.moveUp(PathTrackingReader.java:42)
at hudson.util.RobustReflectionConverter.doUnmarshal(RobustReflectionConverter.java:365)
at hudson.util.RobustReflectionConverter.unmarshal(RobustReflectionConverter.java:269)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:72)
Caused: com.thoughtworks.xstream.converters.ConversionException: : name expected (position:START_TAG <org.jenkinsci.plugins.pipeline.modeldefinition.actions.DeclarativeJobPropertyTrackerAction>@5:97 in java.io.InputStreamReader@3a530a3f) : : name expected (position:START_TAG <org.jenkinsci.plugins.pipeline.modeldefinition.actions.DeclarativeJobPropertyTrackerAction>@5:97 in java.io.InputStreamReader@3a530a3f)
---- Debugging information ----
message : : name expected (position:START_TAG <org.jenkinsci.plugins.pipeline.modeldefinition.actions.DeclarativeJobPropertyTrackerAction>@5:97 in java.io.InputStreamReader@3a530a3f)
cause-exception : com.thoughtworks.xstream.io.StreamException
cause-message : : name expected (position:START_TAG <org.jenkinsci.plugins.pipeline.modeldefinition.actions.DeclarativeJobPropertyTrackerAction>@5:97 in java.io.InputStreamReader@3a530a3f)
class : org.jenkinsci.plugins.workflow.job.WorkflowJob
required-type : java.util.concurrent.CopyOnWriteArrayList
converter-type : hudson.util.RobustReflectionConverter
path : /flow-definition/actions
line number : 5
version : not available
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