It depends on whether you have snap autodelete on or off, and the policy you have set there, also will depend on the volume options try_first is set to.
I think the default is to autodelete at >80% and it will delete scheduled snapshots first and then user created last.
You can either turn of snap autodelete and set it to volume autogrow.
If you just need a copy of the volume you could mount the snapshot and copy the data out that way.
