centernet to tf1.0， train and eval were normal， but get "Key not found in checkpoint" error when executing export_inference_graph.py

System information:
What is the top-level directory of the model you are using: models/research
Have I written custom code (as opposed to using a stock example script provided in TensorFlow): No
OS Platform and Distribution (e.g., Linux Ubuntu 16.04): Linux Ubuntu 16.04
TensorFlow installed from (source or binary): binary
TensorFlow version (use command below): 1.15.0
Bazel version (if compiling from source):
CUDA/cuDNN version:
GPU model and memory:

Describe the problem:
I am doing a tf1.0 centernet thing.
I have added center_net_mobilenet_v2 to model_builders, and train & eval looks pretty normal (by model_main.py), but inference result is strange, all the boxes had a same score!
any one has ideas, really appreciate!