XHR Json call failing for locations_map Google Map display

Hi WordPress team,
I’ve recently done an upgrade to a local community site to WordPress 4.9.8 including all plugins and themes. I’ve just noticed the Google Map is failing to display on https://minstead.org.uk/local-amenities/map/
Debugging this I believe the Google Map API key is all fine but the JS console is reporting:

events-manager.js?ver=5.95:879 Uncaught TypeError: Cannot read property ‘length’ of null
at Object.success (events-manager.js?ver=5.95:879)
at i (jquery.js?ver=1.12.4:2)
at Object.fireWith [as resolveWith] (jquery.js?ver=1.12.4:2)
at y (jquery.js?ver=1.12.4:4)
at XMLHttpRequest.c (jquery.js?ver=1.12.4:4)

…which is due to the XHR call for the location JSON returning empty.
The current XHR URL is https://minstead.org.uk/local-amenities/map/?width=650px&height=500px&town=Minstead&em_ajax=true&query=GlobalMapData&random_id=8cb7b …and I’ve tried playing with various params without any joy.

Contrast this with the Events plugin demo page (https://demo.wp-events-plugin.com/shortcode/) which calls https://demo.wp-events-plugin.com/shortcode/?width=600px&height=400px&scope=future&em_ajax=true&query=GlobalMapData&random_id=60f25 and returns a healthy JSON block.
I’ve also tried resaving Locations but no joy.

Any pointers on how to debug why the XHR call is returning nothing would be appreciated.

Thanks,
Shaun

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