Через раз открывается вкладка "Ресурсы" в админке

Здравствуйте, проблема следующая, при открытии админки в MODX REVO 2.5.1 не подгружается содержимое вкладки «Ресурсы», иногда подгружается, но появляется значок «Загрузка», который не исчезает. Если несколько раз обновить страницу, то всё ок, а после очередного обновления страницы снова не подгружаются ресурсы.

В консоли висит ошибка JS, о том, что указанный в скрипте адрес возвращает ошибку 502, при заходе на этот адрес — никакой ошибки нет, а выводится строка с данными:

POST http://mysite/connectors/index.php 502 (Bad Gateway)
i @ ext-base.js:21
request @ ext-base.js:21
request @ ext-all.js:21
doRequest @ ext-all.js:21
request @ ext-all.js:21
execute @ ext-all.js:21
load @ ext-all.js:21
MODx.grid.Grid @ modx.jsgrps-min.js:5
MODx.grid.RecentlyEditedResourcesByUser @ modx.grid.user.recent.resource.js:46
create @ ext-all.js:21
load @ modx.js?v=f0030b3e:85
(anonymous) @ (index):39
(anonymous) @ ext-all.js:21
b @ ext-all.js:21
modx.jsgrps-min.js:4 Uncaught TypeError: this.mask.addClass is not a function
    at S.onShow (modx.jsgrps-min.js:4)
    at S.afterShow (ext-all.js:21)
    at S.show (ext-all.js:21)
    at Object.show (ext-all.js:21)
    at MODx.onAjaxException (modx.js?v=f0030b3e:122)
    at h.Event.fire (ext-all.js:21)
    at Ext.data.Connection.fireEvent (ext-all.js:21)
    at Ext.data.Connection.handleFailure (ext-all.js:21)
    at f (ext-base.js:21)
    at m (ext-base.js:21)
onShow @ modx.jsgrps-min.js:4
afterShow @ ext-all.js:21
show @ ext-all.js:21
show @ ext-all.js:21
onAjaxException @ modx.js?v=f0030b3e:122
fire @ ext-all.js:21
fireEvent @ ext-all.js:21
handleFailure @ ext-all.js:21
f @ ext-base.js:21
m @ ext-base.js:21
(anonymous) @ ext-base.js:21
ext-base.js:21 POST http://mysitei.com/connectors/index.php?action=element/getnodes&id=n_chunk_category_6&type=chunk 502 (Bad Gateway)
i @ ext-base.js:21
request @ ext-base.js:21
request @ ext-all.js:21
requestData @ ext-all.js:21
load @ ext-all.js:21
expand @ ext-all.js:21
e @ ext-all.js:21
runCallback @ ext-all.js:21
expand @ ext-all.js:21
expand @ ext-all.js:21
(anonymous) @ ext-all.js:21
(anonymous) @ ext-base.js:21
modx.jsgrps-min.js:4 Uncaught TypeError: Cannot read property 'removeClass' of undefined
    at S.onHide (modx.jsgrps-min.js:4)
    at S.afterHide (ext-all.js:21)
    at S.hide (ext-all.js:21)
    at Object.hide (ext-all.js:21)
    at Object.show (ext-all.js:21)
    at MODx.onAjaxException (modx.js?v=f0030b3e:122)
    at h.Event.fire (ext-all.js:21)
    at Ext.data.Connection.fireEvent (ext-all.js:21)
    at Ext.data.Connection.handleFailure (ext-all.js:21)
    at f (ext-base.js:21)
onHide @ modx.jsgrps-min.js:4
afterHide @ ext-all.js:21
hide @ ext-all.js:21
hide @ ext-all.js:21
show @ ext-all.js:21
onAjaxException @ modx.js?v=f0030b3e:122
fire @ ext-all.js:21
fireEvent @ ext-all.js:21
handleFailure @ ext-all.js:21
f @ ext-base.js:21
m @ ext-base.js:21
(anonymous) @ ext-base.js:21
ext-base.js:21 POST http://mysite.com/connectors/index.php?action=resource/getNodes&id=web_6&type=modResource 502 (Bad Gateway)
i @ ext-base.js:21
request @ ext-base.js:21
request @ ext-all.js:21
requestData @ ext-all.js:21
load @ ext-all.js:21
expand @ ext-all.js:21
e @ ext-all.js:21
runCallback @ ext-all.js:21
expand @ ext-all.js:21
expand @ ext-all.js:21
loadComplete @ ext-all.js:21
(anonymous) @ ext-base.js:21
runCallback @ ext-all.js:21
processResponse @ ext-all.js:21
handleResponse @ ext-all.js:21
handleResponse @ ext-all.js:21
f @ ext-base.js:21
m @ ext-base.js:21
(anonymous) @ ext-base.js:21
modx.jsgrps-min.js:4 Uncaught TypeError: this.mask.addClass is not a function
    at S.onShow (modx.jsgrps-min.js:4)
    at S.afterShow (ext-all.js:21)
    at S.show (ext-all.js:21)
    at Object.show (ext-all.js:21)
    at MODx.onAjaxException (modx.js?v=f0030b3e:122)
    at h.Event.fire (ext-all.js:21)
    at Ext.data.Connection.fireEvent (ext-all.js:21)
    at Ext.data.Connection.handleFailure (ext-all.js:21)
    at f (ext-base.js:21)
    at m (ext-base.js:21)
onShow @ modx.jsgrps-min.js:4
afterShow @ ext-all.js:21
show @ ext-all.js:21
show @ ext-all.js:21
onAjaxException @ modx.js?v=f0030b3e:122
fire @ ext-all.js:21
fireEvent @ ext-all.js:21
handleFailure @ ext-all.js:21
f @ ext-base.js:21
m @ ext-base.js:21
(anonymous) @ ext-base.js:21
ext-base.js:21 POST http://mysite.com/connectors/index.php?action=resource/getNodes&id=web_9&type=modResource 502 (Bad Gateway)
i @ ext-base.js:21
request @ ext-base.js:21
request @ ext-all.js:21
requestData @ ext-all.js:21
load @ ext-all.js:21
expand @ ext-all.js:21
e @ ext-all.js:21
runCallback @ ext-all.js:21
expand @ ext-all.js:21
expand @ ext-all.js:21
(anonymous) @ ext-all.js:21
(anonymous) @ ext-base.js:21
modx.jsgrps-min.js:4 Uncaught TypeError: Cannot read property 'removeClass' of undefined
    at S.onHide (modx.jsgrps-min.js:4)
    at S.afterHide (ext-all.js:21)
    at S.hide (ext-all.js:21)
    at Object.hide (ext-all.js:21)
    at Object.show (ext-all.js:21)
    at MODx.onAjaxException (modx.js?v=f0030b3e:122)
    at h.Event.fire (ext-all.js:21)
    at Ext.data.Connection.fireEvent (ext-all.js:21)
    at Ext.data.Connection.handleFailure (ext-all.js:21)
    at f (ext-base.js:21)

Никаких изменений на сайте не производил, в ядро не лазил, дополнения не устанавливал. В чём проблема?