When I try and use the “Visitor log” export as csv/tsv I am getting an error
There is an error. Please report the message and full backtrace in the Piwik forums (please do a Search first as it might have been reported already!).
Notice: Array to string conversion in /var/www/vhosts/x/subdomains/stats/httpdocs/core/DataTable/Renderer/Csv.php on line 267
Looking at the code and doing a dump of that function formatValue($value)
The value being passed is an array
Array ( [2] => Array ( [customVariableName2] => page [customVariableValue2] => 811 ) )
Which is causing the issue 
Seems to be a small flaw in the csv export routine - any ideas welcome whilst I look at it.