Successfully converted: 4K HDR to 4K 60FPS 8 Bit SDR but now it plays in slow motion

[4K@60FPS]

I wanted to ask you maybe you know how to fix this issue?

No details about the input.
No details about your settings
-> no clue what you are doing, but if the playback is slow then it might be that you changed the frame rate from for example 24/25/50/30fps to 60fps just by changing the frame rate flag and not by creating new frames,...

Cu Selur

I am using Vapoursynth and am converting 23 fps video  into 60 fps in Vapoursynth / frame interpolation / Interframe 60 fps. I am not sure why the video plays in slow motion after conversion, other videos that I converted were converted ok.

My input is: UHD 4K HDR file 23 fps but I want the output of the same video in 60 fps to 4K SDR 8 BIT. I am using these settings:  Vapoursynth / frame interpolation / Interframe/ 60fps smooth;  Vapoursynth /color/ HDR10 to SDR; x264 5.2, bitrate 35000 kbs. 

Other UHD 4K HDR videos that I converted were fine but others  after conversion played only in slow motion, I am not sure what's the problem