There’s a known limitation in the WordPress builtin export/import feature that is preventing some information from being imported correctly, when using the exported XML file. Usually what fails to import are the data from fields that repeat, like the regions information or markers information. This happens because of line breaks in the content, usually in the Tooltip Content field or the Action Content field. Right now there isn’t an easy fix, but one way to workaround this would be to make sure none of your text areas in these fields includes line breaks.
The technical explanation
The map data is serialized (a PHP feature) and saved in a meta field. When serialized, the content has some information regarding the length of the fields and this length is ignoring the line breaks, so the number is wrong. This causes an error when unserializing the data. Related trac ticket. We’re trying to improve this, but if you come across this issue, try the workaround mentioned above. If the problem persists, write us describing the issue.