FPS drops to unplayable (Metro: Last Light)

Sinking to 13 FPS during firefights. Average fps on the levels jump from 90 to 28. Config FX-6100 3.3.GTX1050ti GHz 4 GB, 8 GB RAM. Version of the game Redux. Passed her when she came to the old its a GTX550ti, the lag was not particularly. What could be the problem?