Laggy playback and handling of AVC video

Got a video file recorded using OBS and Blackmagic Decklink 4K card. It was encoded using GPU and ended up in format like this:

Video ID                          : 1 Format                      : AVC Format/Info                 : Advanced Video Codec Format profile              : Main@L4.2 Format settings             : CABAC / 2 Ref Frames Format settings, CABAC      : Yes Format settings, ReFrames   : 2 frames Codec ID                    : avc1 Codec ID/Info               : Advanced Video Coding Duration                    : 46 min 50 s Bit rate mode               : Constant Bit rate                    : 35.0 Mb/s Width                       : 1 920 pixels Height                      : 1 080 pixels Display aspect ratio        : 16:9 Frame rate mode             : Constant Frame rate                  : 60.000 FPS Color space                 : YUV Chroma subsampling          : 4:2:0 Bit depth                   : 8 bits Scan type                   : Progressive Bits/(Pixel*Frame)          : 0.281 Stream size                 : 11.2 GiB (100%) Color range                 : Limited Matrix coefficients         : BT.470 System B/G

I have an 8 core xeon and 1080ti gpu, but program lagged hardly when I tried to edit something. Playback lagged too, cpu load was near 80%. What's wrong? Should I update some codecs or settings? CUDA rendering works fine, I checked.