Hi,
Could you try to change this line:
bind ( uri(concat(str(?protocol),"://",?username,":",?password,"@",str(?host),":",str(?port),str(?queryPath))) as ?connectionURI )
to
bind ( coalesce(uri(concat(str(?protocol),"://",?username,":",?password,"@",str(?host),":",str(?port),str(?queryPath))), "") as ?connectionURI )
SERVICEes with a variable in the service IRI position are not quite standardised so there could be differences in behaviour. Since ?connectionURI is bound to an expression, and the expression evaluation could in principle result in an error (thus leaving the variable without a value), Stardog cannot immediately use it as the service IRI. Admittedly, the error message isn't clear enough.
If it doesn't solve it, we'll try to reproduce locally,
Pavel