UCSS error message

Hi,
UCSS seemed to be running find (v4.0 & v4.1) but no longer. Response = /null/

Error message in debug log:
06/28/21 11:41:56.877 xxx.xxx 1 VzE] [Cloud] response ok — array (
‘ucss’ => ‘/* null */’,
‘msg’ => ‘UCSS generator error: Protocol error (Page.navigate): Invalid parameters url: string value expected’,
)

Any idea?

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