Frame rate drop when play public mission

[SpaceAlienNinja]

My PC may be an old potato but it got 24-30 fps regularly
I stop playing for sometime and came back because Loki Unvaulted so I decide it's time to grind
at the start in my ship I got constant 17 fps.... weird... I restart the game 24-30 fps on my ship OK this is working
going into Exta mission(orokin cell farm mission) got 14-15 fps on loading screen.... what... after it loaded I got 2 fps

....2 constant fps....

WTF... I open Task manager CPU Usage at 36-40

I try going again in solo ....30 fps....
maybe it just 1 time thing ? try dojo... 16 fps
try public exta again 2 fps.... anyone know what's happen ?

Win 7
I5-4430 3.00 GHz
Ram 8.00 GB
Nvidia Geforce GTX 960