Hi,
It is the pipeline linkage in deepstream-app. If it cannot have 60fps, may not achieve 60fps in running deepstream-app. Please execute nvpmodel -m 0 and sudo jetson_clocks to run in max performance. See if this helps.
If your source supports UYVY, you may try nvv4l2camerasrc and run the pipeline
$ gst-launch-1.0 nvv4l2camerasrc device=/dev/video1 bufapi-version=1 ! 'video/x-raw(memory:NVMM),width=1920,height=1080,framerate=60/1,format=UYVY' ! nvvideoconvert ! 'video/x-raw(memory:NVMM),format=NV12' ! fpsdisplaysink text-overlay=0 video-sink=nvoverlaysink -v