In some cases, when reviewing your data in the Analytics section of the Opticks app you can find some rows with the label 'Unknown' when you group the data by specific dimensions.
The main reason for this happening is because, when sending clicks to Opticks for analysis, some variable was not correctly filled with a value.
The second reason for the 'unknown' row is actually more important and more necessary to fix.
The variables subpublisher_id, var1, var2, var3 and var4 are used to feed data to Opticks and make it available as a dimension to filter by in the Analytics section of your Dashboard. This means that they are meant to be used for dimensions that have a limited cardinality, meaning that they are NOT meant for UNIQUE values.
What happens when you feed unique values (e.g. some unique identifiers) into any of those variables? Opticks will receive just a single occurrence of each possible value. When that happens, all those different values with just one occurrence will be "flattened" inside an UNKNOWN value after a short period of time.