Irregular time for object detection with VIM3 NPU

I have yolov4 weights file converted to NPU now.
But when i test this file for test Object detection on khadas NPU, detection time happens irregulary.
Sometimes it is 5 or 6 times different from the original times…
So i want to know why detection time happens irregulary on khadas NPU.
Please let me know why this reason is happend..

Ubuntu 20.04 LTS

  1. Network size 864x416

    (detection for) original time = 350ms

    (detection for) increased time = 16210ms

  2. Network size 416x416

    (detection for) original time = 160ms

    (detection for) increased time = 8410ms