Help No vibration when receiving message/notification from Facebook messenger

When i receive a notification from Facebook messenger, it plays the sound,. but does not vibrate, which is really annoying when i use silent mode, as its impossible to tell if i get a message

I have enabled the vibration settings everywhere, in system and in the app itself? All other apps seem to vibrate when receiving notifications...

Anyone have any ideas on how to fix this?

Thanks in advance =)

running, stock 2.3.5
I am having the same problem on my S5. I fixed it in the previous OS version by disabling the Chat Heads feature, but the problem returned when the OS upgraded to Marshmallow.