Event though it's controled by root URL its set at the time the task is created.
First check if this is the problem:
select
COUNT(*) from dbo.TaskResponse
where URL like 'http://serverOLD'
Then backup DB and fix with this:
update
dbo.TaskResponse
set URL = REPLACE(URL, 'http://serverOLD','http://serverNEW')
where URL like 'http://serverOLD%'