Welp, I just can't get promotion.
I've completed 2nd rank of Immortal Flame log at around lvl 38. I was Flame Sergeant First Class at that time. When I went to take promotion to Chief Flame Sergeant, it said about trial from commander. Well, I waited for 44 to take this trial (Shadow Uncast), completed it and was able to get promotion to Chief Flame Sergeant. Now, when I try to get promotion to Second Flame Lieutenant, it says that I need to complete log (which I have done long ago) and complete trial from Commander. There is no other trial from Commander available so it looks like I'm stuck.