Problem dragging widgets

I have started to experience an issue with Elementor. I can edit existing widgets fine and insert one of my saved sections into a page. However I can’t drag a widget from the left and drop it into an existing or new column section. As soon as I grab it I see a red circle with a line through it and I can’t move it across. So I can’t create any new content.

I deactivated all my plugins but it didn’t fix the issue. I think the problem might be down to the Wordfence plugin which I recently installed on my staging URL (but not on an old local test version which still works ok). I deactivated and deleted Wordfence but I noticed a note on your FAQs about purging caching plugins. I’m not sure how to do that, although I did notice on PHP Admin that there are quite a few files starting wf which I thought would have been deleted but still are there. I am not confident looking at this view, however, as I am a beginner so not sure if OK to just delete these. E.g. I am not sure how to edit the config.php file within PHP Admin.

Is there a known problem with Elementor and Wordfence? If so, do you have any suggestions for alternatives?
Any advice enormously appreciated.

== Server Environment ==
Operating System: Linux
Software: Apache/2.4.18 (Unix)
MySQL version: 5.5.5
PHP Version: 5.4.45
PHP Max Input Vars: 1000
PHP Max Post Size: 64M
GD Installed: Yes
Elementor Library: connected

== WordPress Environment ==
Version: 4.6.1
Site URL: http://global-laundrylockers.co.uk
Home URL: http://global-laundrylockers.co.uk
WP Multisite: No
Max Upload Size: 64 MB
Memory limit: 40M
Permalink Structure: /%postname%/
Language: en-US
Timezone: 0
Admin Email:
Debug Mode: Inactive

== Theme ==
Name: GeneratePress Child
Version: 0.1
Author: Thomas Usborne
Child Theme: Yes
Parent Theme Name: GeneratePress
Parent Theme Version: 1.3.40
Parent Theme Author: Tom Usborne

== User ==
Role: administrator
WP Profile lang: en_US
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.79 Safari/537.36 Edge/14.14393

== Active Plugins ==
Duplicator
Name: Duplicator
Version: 1.1.18
Author: LifeInTheGrid

Elementor
Name: Elementor
Version: 0.10.3
Author: Elementor.com

Formidable
Name: Formidable
Version: 2.02.07
Author: Strategy11

GP Premium
Name: GP Premium
Version: 1.2.90
Author: Tom Usborne

Responsive Lightbox
Name: Responsive Lightbox
Version: 1.6.9
Author: dFactory

Responsive WordPress Slider – Soliloquy Lite
Name: Responsive WordPress Slider – Soliloquy Lite
Version: 2.5.0.7
Author: Soliloquy Team