July 2019
IGF: As soon as you reach level 10 queue for story mode Black Talon or Esseles. If you don't do this before you reach level 15, I know of no way to complete IGF, which is a prerequisite for WLFG.
WLFG: Queue for master mode Black Talon or Esseles. Ask players to stay in group after finishing. You need to click [Accept] before anyone drops group.
I have only tested these workarounds on the Imperial side.
July 2019
I just completed IGF on my level 18 Juggernaut. I didn't do it before 15 as I normally level past that first but when I got to the fleet, I accepted the mission for IGF and completed it and turned it in.
The main thing is that in order to get credit, you have to have all possible FPs accepted which for me was 22. So when you open the GF window for PvE, ensure that you have all possible FPs selected which it will show on the bottom right corner.
If not then you won't get credit.
July 2019
July 2019 - last edited July 2019
Do you have a solo instance version of a Flashpoint in your Mission log?. I do know that if you have for example solo mode for Black Talon Solo Mode or The Esseles Solo Mode in your log will cause the issue.
You cannot have both a solo mode Flashpoint and a group Flashpoint in your mission log at the same time or it will not give credit for Introduction to Group Finder.