Hi @lkhphuc @tom. A common cause for this is converting the model with a version of Pytorch less than 1.3.0. As of present, only models converted with the latest pytorch version would load.
See my latest tutorial on Pytorch Mobile including an easy to reuse open source image recognition example.
This provides a useful guide
https://heartbeat.fritz.ai/pytorch-mobile-image-classification-on-android-5c0cfb774c5b 15