Symptoms
Additional resources for add-on hosting plan are not available in Online Store. The same service plan resources are shown correctly when plan is displayed "stand-alone", not as the second step of the purchase scenario.
Cause
The issue is caused by the bug with id #PBA-82308 ("Additional resources are not shown for the second plan").
Resolution
As a workaround you can remove the records from RESOURCE_CATEGORY parameter of the first hosting screen. If such workaround is not acceptable, please contact Odin Technical Support.