Hello Mauro,
Replacing your MX85 with MX84 will not affect your configuration. However, please keep in mind that the maximum runnable firmware version for MX84 is MX18.107.10. So, any new features available from the MX18.211+ version will not be available while using the MX84.
Also while moving the cables on the LAN interfaces please ensure you are plugging into the right LAN ports and enabe the site to site VPN
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