Hi Tantcy,
Thanks for using syncfusion products.
We have prepared a simple sample to demonstrate the behavior of the UploadBox and UploadProgress in both master and content pages. The sample works fine without any issues in our end.
Kindly download the sample from the following link,
UploadBox-Masterpage-1078354228.zipIf the issue exists still, could you please modify the attached sample to reproduce this issue and share with us? So that we would investigate more on this and provide an efficient solution.
Regards,
Varalakshmi R.S