After upgrading from 7.6.2 to 7.6.4, the link functionality in the Report module seems to be broken.
index.php?module=Opportunities&action=DetailView&record=
is the link that is created when the “Link” field is tagged in Reports module.
The record field should have the id of the record in the module behind the = sign. Obviously, click on the link results in a blank page 
This used to work in 7.6.2!
I have been looking into this.
Looking at “<SUITECRM_DIR>/modules/AOR_Reports/AOR_Report.php” line 696
$html .= "<a href='" . $sugar_config['site_url'] . "/index.php?module=".$att['module']."&action=DetailView&record=".$row[$att['alias'].'_id']."'>";
this is the piece of the function build_report_html that generates the links html for the report.
at part after record
record="".$row[$att['alias'].'_id']."'
lets say I had a dashlet on my homescreen that returns tasks
$att[‘alias’] will return tasks
.’_id’ adds _id to the end of tasks to make tasks_id
and so will resolve to $row[tasks_id]
I get an error reporting
Undefined index: tasks_id in <suitecrm_dir>/modules/AOR_Reports/AOR_Report.php
looking at an example of $row arrays (each row to render in the report)
Array
(
[Date_Created0] => A Date
[Subject1] => 'A Subject'
[Description2] => 'Description'
[Projects3] => UUID For Project
[Due_Date4] => Date
[Status5] => Staus
[Priority6] => Priority
[Assigned_to7] => UUID for the user assigned to this task
)
there is no task_id index in this array.
the $row array seems to change between the while statement at line 633 and line 690 as the output of $row here
Array
(
[id] => 1a3g46sa-34ac-v425-4f43-654gbx87fe5f
)
does return UUID’s (this isn’t the real UUID I got back, I changed it for data protection reasons)