400 error on edit properties spotlight position

• Apache, PHP5.6 on Joomla 3.7
• Template jr_directory or jr_builder (both same)
• Running live environment (localhost install doe snot work at all?)

Hi,

When i click on the spotlight "edit" icon to select a module position the site throws a 400 error, not loading an external file from themepro server (see attachment). Problem persists on a fresh install Joomla without any additional plugins installed.
Do you guys have any idea what could be the issue?

Jasper