Looks like the boxydash repo has been abandoned since 2016, so I am not too surprised that there are some incompatibilities.
Maybe there’s someone who wants to pick up the deveopment of it 
I would strongly suspect, that the error stems from the module using short open tags, i.e. <? instead of <?php in the view script just like in this issue here in GraphDash.
This has been deprecated for years and with the 2.8 we dropped the support for it.
PS: Please wrap the stacktrace in a code block as described in out markdown guidelines to make them more readable in the future - thanks!