The Storage capacity can be adjusted.
/// <summary>
/// The amount of gigabytes UBA is allowed to use to store workset and cached data. It is a good idea to have this >10gb
/// </summary>
[XmlConfigFile(Category = "UnrealBuildAccelerator")]
[CommandLine("-UBAStoreCapacityGb")]
public int StoreCapacityGb { get; set; } = 40;
So go to your BuildConfigurationXML and add this under the root:
<UnrealBuildAccelerator>
<StoreCapacityGb>64</StoreCapacityGb>
</UnrealBuildAccelerator>