Hey Sam,
I opened the devtools console and there were three issues - jquery.ui.widget, jquery.ui.core and jquery.ui.position. I've included them below. My guess is that some extension is calling the deprecated modules and the toolbar is failing which causes the blue space to be removed. I've tried a bunch of stuff and some removed the blue space but also removed the toolbar so there must be some sort of relation between the two. Do you have any ideas about this issue or any solutions?
VM303:126 This page is using the deprecated ResourceLoader module "jquery.ui.widget".
(anonymous) @ VM303:126
(anonymous) @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:161
fire @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:45
add @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:45
always @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:46
runScript @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:160
checkCssHandles @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:161
execute @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:162
implement @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:168
(anonymous) @ VM303:126
(anonymous) @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:4
globalEval @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:4
(anonymous) @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:165
requestIdleCallback (async)
asyncEval @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:165
work @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:166
enqueue @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:163
load @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:169
(anonymous) @ index.php?title=Main_Page&action=edit:10
startUp @ load.php?debug=false&lang=en&modules=startup&only=scripts&skin=vector:27
script.onload.script.onreadystatechange @ load.php?debug=false&lang=en&modules=startup&only=scripts&skin=vector:28
load (async)
(anonymous) @ load.php?debug=false&lang=en&modules=startup&only=scripts&skin=vector:27
(anonymous) @ load.php?debug=false&lang=en&modules=startup&only=scripts&skin=vector:28
VM303:166 This page is using the deprecated ResourceLoader module "jquery.ui.position".
(anonymous) @ VM303:166
(anonymous) @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:161
fire @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:45
add @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:45
always @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:46
runScript @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:160
checkCssHandles @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:161
execute @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:162
implement @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:168
(anonymous) @ VM303:166
(anonymous) @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:4
globalEval @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:4
(anonymous) @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:165
requestIdleCallback (async)
asyncEval @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:165
work @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:166
enqueue @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:163
load @ load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=13nadqn:169
(anonymous) @ index.php?title=Main_Page&action=edit:10
startUp @ load.php?debug=false&lang=en&modules=startup&only=scripts&skin=vector:27
script.onload.script.onreadystatechange @ load.php?debug=false&lang=en&modules=startup&only=scripts&skin=vector:28
load (async)
(anonymous) @ load.php?debug=false&lang=en&modules=startup&only=scripts&skin=vector:27
(anonymous) @ load.php?debug=false&lang=en&modules=startup&only=scripts&skin=vector:28
VM303:121 This page is using the deprecated ResourceLoader module "jquery.ui.core".
Please use "mediawiki.ui.button" or "oojs-ui" instead.