Hi MattEJ, I'm an end user like you. Are you paying for the next aware subscription? Are you using the NEST app or the GOOGLE Home app?
If you have the nest aware subscription and this is happening then I think your next step is to contact Google Support for help. This is a user forum and Google techs do not respond here.
Here is the link:
I'm pretty sure if you are not paying for the subscription then you only get 3 hours of history from Google. It has nothing to do with your local memory as the clips are stored in the Google cloud and not on your phone. If it was working before then it might be because Google gives everyone a 30-day trial subscription and maybe you are past the 30 days?
If you are interested here is the link. https://store.google.com/us/product/nest_aware?hl=en-US
Hmmmm, that is strange. I don't think you will get your answer here as this is just a user forum. For this I think you need to reach out to Google tech support and ask what is going on. Here is the link to open a ticket. You may need the serial number of our camera.
Please come back and let us know what happened.