Saying Framestore full when it's not

Anyone know why this pops up? I have plenty of space left. It’s a biggish batch with lots of nodes caching, but no where near filling the framestore, most of it’s cached already anyway. This usually happens when I’m in to the final third of the space I have left. Very annoying.

If I use a write file node rather than normal render node it renders without complaint.

What happens if you render out the cache nodes as opposed to caching the nodes? I wonder if flame just gets overwhelmed if it’s trying to cache 20 renders at the same time and panics.