PoN creation error

I'm trying to create a PoN but keep getting the following error in the merge_pons stage:

message: Workflow failed
causedBy:
message: Call input and runtime attributes evaluation failed for merge_pons
causedBy:
message: Invalid parameters for engine function sub: (Failure(java.util.NoSuchElementException: key not found: totSizeFloat),Success(WomString(..*)),Success(WomString())).
message: key not found: stringDiskSizeGB
message: Can't index Success(WomInteger(7)) with index Success(WomInteger(0))
message: key not found: sizeOfPonFile

https://portal.firecloud.org/#workspaces/broad-firecloud-wuclonal/SandBox_Analysis/monitor/93db83d4-6b54-456a-9f12-ccc91da67f51/f207c7bd-bf88-4e0f-b095-9fdacd6dcae7

Do you know what might be causing this?

Thanks