Runtime error: Invalid Rank 6

## ❓Question

I am trying to train an updatable coreml model on the device. The model is a classification model trained on 6 classes and accepts an input of shape (1,3). I could successfully convert the model from Keras and run predictions on it. However, when trying to train the model on the device I get the following error:
**[espresso] Training kernels not enabled for engine: 100
libc++abi.dylib: terminating with uncaught exception of type std::runtime_error: Invalid rank: 6**
Not sure where I am going wrong.

Attaching a screenshot of the mlmodel .

## System Information
MacOS Catalina (10.15.6)
Xcode 11.2.1
iOS 13.3
Coremltools 4.0b2
Python 3.7
Tensorflow 2.2

The issue names no repository file, test, or entry point. Start by reproducing on the listed coremltools, TensorFlow, Xcode, and iOS versions, then investigate device training for the attached model and the reported “Invalid rank: 6” error; done means identifying the cause or a documented compatibility limitation.

Written by the indexing model from the issue text.