This is down to the change in how complex variables are resolved in PHP 5 vs 7. See the section on Changes to variable handling here: http://php.net/manual/en/migration70.incompatible.php
The difference is that the expression:
$this->links->$data[$te]['attributes']['ID']
is evaluated like this in PHP 5:
$this->links->{$data[$te]['attributes']['ID']}
and like this in PHP 7:
($this->links->$data)[$te]['attributes']['ID']
See https://3v4l.org/gB0rQ for a cut-down example.
You'll need to amend your code to be explicit, either by using {}
as appropriate, or by breaking it down into two lines. In this case, where you've got code that works fine in PHP 5, pick the former, since it will mean the behaviour stays consistent in all versions of PHP.
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