Understanding JSON response (syncId, clientId, Timings, etc) to diagnose JS


I’m having a big problem with a series of Vaadin portlets deployed on WebSphere Portal where a certain xhr request is not returning JSON but an empty response under certain circumstances I haven’t been able to pinpoint exactly.

To be honest I’m not sure if this is caused by Vaadin or by the Portal, but wanted to ask about the request and response in hopes that any information can help me diagnose the problem.

The request that’s being sent is


And under normal circumstances the response the browser gets is

for(;;);[{“syncId”: 1, “clientId”: 0, “changes” :
, “state”:{}, “types”:{}, “hierarchy”:{}, “rpc” : , “meta” : {}, “resources” : {}, “timings”:[629, 629]

But there are times when that request returns an empty response which causes an “invalid JSON” message, and if I click on the message the page reloads and shows the message, so the application is now stuck in a loop until I close the session, or load the home page URL manually.

Any information about this request is appreciated.

Thank you.