Save model parameters on each checkpoint

I would like to save the model (.pb, .h5) parameters on each checkpoint as we would like
to compare the various stages of training outside of the ray/rllib framework and the
models are relatively small. It is not possible to know ahead of time how many iterations
are needed for training at the moment.

I have confirmed saving at the end of training works:

from ray import tune
from ray.rllib.agents.ppo import PPOTrainer
from ray.tune.trial import ExportFormat

tune.run(PPOTrainer,
config={“env”: “CartPole-v0”},
export_formats=[ExportFormat.MODEL, ExportFormat.H5, ExportFormat.CHECKPOINT],
local_dir=‘cart_outputs3’,
stop={“training_iteration”: 1}
)

PPO_CartPole-v0_91fad_00000_0_2021-07-14_09-14-54
├── checkpoint
│ ├── checkpoint
│ ├── model.data-00000-of-00001
│ ├── model.index
│ └── model.meta
├── events.out.tfevents.1626250494.velocity
├── model
│ ├── events.out.tfevents.1626250523.velocity
│ ├── saved_model.pb
│ └── variables
│ ├── variables.data-00000-of-00002
│ ├── variables.data-00001-of-00002
│ └── variables.index
├── params.json
├── params.pkl
├── progress.csv
└── result.json

(First problem is that the .h5 file is not created despite it being an available export option)

Now we use Tune:

results = tune.run(args.run, config=config, stop=stop, checkpoint_freq=2,
export_formats=[ExportFormat.MODEL, ExportFormat.H5],
num_samples=1, checkpoint_at_end=False)

But in this case nothing else appears in the checkpoints at all.
checkpoint_000002
├── checkpoint-2
└── checkpoint-2.tune_metadata

In a previous version of Ray (I think 0.8.0) - setting
,“checkpoint_freq”:2
,“checkpoint_at_end”: True
in the config and using run_experiments would create the model data under each checkpoint directory:
run_experiments({“EnvName”: myconfig})

So how can one save the model parameters (TensorFlow in this case) - to .pb or .h5 at each
checkpoint (the model is small) using ray.tune? Many thanks!

As an additional point, using ray==1.4.1 on Mac OS X. Is saving a model down in recoverable format (pb, hdf5) at checkpoints a supported feature? Is there any other information needed? I am kind of stuck at this point. Cheers.