After launching an agent it keeps hanging with the following text :

[05/06/20 20:34:24] [SSH] Starting agent process: cd "/var/lib/jenkins" && java -jar remoting.jar -workDir /var/lib/jenkins May 06, 2020 8:34:25 PM org.jenkinsci.remoting.engine.WorkDirManager initializeWorkDir INFO: Using /var/lib/jenkins/remoting as a remoting work directory May 06, 2020 8:34:25 PM org.jenkinsci.remoting.engine.WorkDirManager setupLogging INFO: Both error and output logs will be printed to /var/lib/jenkins/remoting <===[JENKINS REMOTING CAPACITY]===>channel started Remoting version: 4.3 This is a Unix agent

This happens since a couple of weeks

jstack reports a deadlock in attachment :

Found one Java-level deadlock:
=============================
"pool-1-thread-4 for channel id=17236":
waiting to lock monitor 0x00007fbd8c015bc8 (object 0x000000076e658428, a hudson.slaves.SlaveComputer$SlaveInitializer$1),
which is held by "Channel reader thread: channel"
"Channel reader thread: channel":
waiting to lock monitor 0x00007fbd9401aed8 (object 0x000000076ded1cc8, a hudson.remoting.RemoteClassLoader),
which is held by "pool-1-thread-4 for channel id=17236"

On april 3 2020 in commit https://github.com/jenkinsci/jenkins/commit/3262d8b7cfbdd1a2e026ad34644e0f9607f5724d  

a new synchronized  method was added that is partly the cause of this deadlock .See line 1026 in main/java/hudson/slaves/SlaveComputer.java