Precondition:
Jenkins 2.277.4
Ubuntu 20.04.2 LTS
openjdk version "11.0.11" 2021-04-20
Problem: I have a Freestyle Job For First time all the done changes are saved (At this moment 'Save' and 'Apply' buttons are at the mid bottom of the page) Next time If I come to do some more changes and try to save, it doesn't work AND no error at all neither in browser 'console' or 'network' (At this moment 'Save' and 'Apply' buttons are at the left bottom of the page)
This issue is similar to this issue raised in Jenkins jira https://issues.jenkins.io/browse/JENKINS-65142
It will be same as: JENKINS-65142, as a result of tables to divs migration JENKINS-64072.
This will affect any Jenkins upgrades to 2.277.1+
Read the upgrade guide and follow the procedures. Check the broken plugins dashboard
It may still be a matter of trial and error if your plugin has not already been identified. Be sure to upgrade all plugins which you can first, then diagnose.