There were changes to the Solr schema for the usage statistics core in DSpace 3, 4 and 5. Usage statistics documents from before the respective upgrades are not changed accordingly at the moment, which may cause problems when code expects documents to conform to the current schema.
This is an umbrella issue; I'm going to set up sub-issues for the actual problems.
This was discussed in the developers' meeting on 4 March, starting around 20:33 in the transcript: http://irclogs.duraspace.org/index.php?date=2015-03-04
|Pre-3 Solr usage stats do not contain uid field||Closed||Unassigned|
|Pre-5 Solr usage stats geo information may get lost when upgrading to 5||Closed|