"Accept Invitation Failed"

[Yazuken]

Someone PLEASE help me figure out why this is happening. I am at my witts end! Whenever I try to invite a friend for SWF they get the message "Accept Invitation Failed. The invitation could not be accepted". The same happens if they invite me. The game gives absolutely no other details as to why this error is ocurring!

They ARE on my friends list.
It shows them as online in-game ( but not as currently playing, strangely enough )
It shows them online and in dead by daylight in the steam overlay.
Software and router firewalls are disabled.

Things I've already tried:

1. forwarding most commonly used steam ports.
2. File integrity check ( 100% passed )
3. Doing one match with randoms and then trying to invite.
4. Tried both me inviting them and them inviting me, same error message for both of us.
5. Uninstalled and reinstalled Dead By Daylight completely.

Am I missing something here? If someone could please help me find out why its doing this, I would be so grateful.

[Yazuken]

UPDATE

Small work-around found ( May only work temporarily though, or work sometimes and sometimes not ) : Deleting and then re-adding the player which you wish to invite or have invite you to a match from your steam friends list seems to work.

Ridiculous way to have to go about it. But its some kind of solution ( or semi-solution ) for anyone having this problem. If anyone knows anything better, please feel free to contribute.