For faster initial connection times, TRAMP stores previous connection properties in a file specified by the user option tramp-persistency-file-name.

The default file name for tramp-persistency-file-name is ~/.emacs.d/tramp.

TRAMP reads this file during Emacs startup, and writes to it when exiting Emacs. Delete this file for TRAMP to recreate a new one on next Emacs startup.

Set tramp-persistency-file-name to nil to disable storing connections persistently.

When TRAMP detects a change in the operating system version in a remote host (via the command uname -sr), it flushes all connection related information for that host and creates a new entry.