I get “Sending Data to the Server” message for about 15 minutes when I try to submit the InfoPath form in SharePoint 2013

I use SharePoint 2013 with 3 servers.One front end, one back end (SQL) and one Workflow/OWA server.

I built a custom InfoPath form with Workflow. It worked perfect until a few days ago when a problem emerged.

Every time I try to submit the form I get "Sending Data to the Server" message for about 15 minutes. The form gets submitted, but the workflow never starts.

I tried to republish the InfoPath form and the workflow, but it did not do any good. The rest of the forms I have are working fine, but I built them using SP 2010 platform.

Please help!