Category tree not displaying when adding new categories

[Gamestech]

Hi all,

 

Recently upgraded to Prestashop 1.6 and it appears that the $699 we spent on support was a complete waste of money, after waiting 10 days to get assistance, they've said it falls outside the scope of the contract and are refusing to assist.

 

With Prestashop in dev mode, if a user goes into categories>add category where you select a parent category for the new category the tree does not display at all.

 

It throws no errors (other than a JS 'tree is not defined' in the console) so I'm lost as to where to start to find out the issue.

 

The site is currently in the middle of theme development, with test data etc so clean install not really an option.

 

Does anyone have any thoughts on where to start debugging an error which doesn't display any details?

 

Thanks in advance.