I can't duplicate the problem as described,. Can you provide more details so that others can duplicate the problem?
As far as I can tell from the ssh-credentials plugin source code, there are no references to HTML tables in any of the UI components. I don't see how it could cause a regression in 2.277.1 job configuration. I confirmed that my freestyle and pipeline jobs that use ssh credentials can be saved with 2.277.1.
If rollback to 1.18.0 resolved the issue, then it is not a tables to divs issue. 1.18 was released 15 months ago with no changes related to tables to divs. 1.18.1 was released 2 months ago and only changed test infrastructure, not code functionality.
I think something else is the root cause of the failure to save that configuration. Could you assure that you've used the instructions in the Jenkins 2.277.1 upgrade guide and in the table to div layout migration to investigate the issue? If that does not bring you to a complete solution, then include the detailed information in this issue. That should include the precise list of plugins installed and the type of job that is failing to save.