In your Encompass account it is possible to archive meters so they no longer display in your meters list. Next to each meter in your meters list is an eye icon with a line through it. If you click that icon the meter will disappear from the meters list and be moved into the meters archive.
To un-archive the meter you need to click the "Show" link at the bottom of the meters list. That will display all of the meters in the archive.

To add an archive meter back to the meter list, click on the eye icon next to the archived meter. That will move the meter back to your meters list.