OK have followed all links and only guess is that the problem is related to being a subdomain. Taxonomy-based markers for nodes and role-based markers for users look perfect out-of-the-box on the predefined 'map/node' and 'map/user' but when want to slightly customize using views get nothing - i.e. blank page.
Yes this is in a test subdomain, view looks fine with only one marker type via node type marker until switch to gmap style taxonomy markers or on usermap from single marker to role based markers.
Is it the subdomain test.domain.com and is there a fix?