Tensorflow 2 Object Detection API - Training MobileNet v2 from scratch

I initially followed this tutorial to fine tune a SSD MobileNet v2 320x320 model from the TF2 model zoo.

However, I want to try training this MobileNetV2 model with a depth multiplier of 0.75. To do this, I understand that I need to retrain the MobileNetV2 model 'from scratch'. So I downloaded the COCO2017 dataset, with the intent to use this config file to train the model. This config mentions that it was trained from an ImageNet checkpoint, so I retrieved a MobileNet checkpoint trained on ImageNet checkpoint with dm=0.75 from here. However, the checkpoint files in this seem to be a different format to the checkpoints provided with the pre trained models on the model zoo? Eg, the model zoo models provide checkpoint, ckpt-0.data-00000-of-00001 and ckpt-0.index, whereas the imagnet checkpoint is missing the 'checkpoint' file.

When I try to train the model on any dataset using the downloaded config and ImageNet checkpoint, I get an error that the checkpoint is expected to be an object-based checkpoint?

I've uploaded my pipeline.config (I had to change the extension to .txt to upload it), from when I tried to train the model on a simple dataset with only one object class.

pipeline.txt