Issue Unable to increase disk space for subscription

[fliegerhermi]

Hi.
A reseller has 1 GB used; 20 GB available disk_space.
When I try to increase a subscriptions Disk_space from 0MB to 1 GB I get the following error message:

plesk bin subscription_settings --update xxxx.de -disk_space 1G
An error occurred while updating domain settings: Cannot set limit 'disk_space' value to '1073741824': Unable to allocate the required amount of resources (1 GB Disk space). Only 0 MB Disk space are available.

I think this must be a bug, because the reseller has no overusage. Any idea? Thanks

OS: Ubuntu 18.04.4 LTS
Product: Plesk Obsidian Version 18.0.28