If the status for an Azure subscription is displaying in a 'Warning' state, clicking on the status within the Subscription asset list (pictured below) will reveal further details as to the cause.
If the further details show the following message, 'Asset collection has failed for more than past 24 hours.' this indicated that asset collection has not been recorded for 24 hours. Often these issues will self-heal before the next collection cycle and the Subscription status will return to 'Healthy'. If the warning is shown for longer than 48 hours, please log a support case via the support portal.
NOTE: A known edge case currently exists where subscriptions may report a 'Warning' state even if the configuration is correct and asset collection is successfully occurring under the subscription. A planned fix for this issue is currently under development. If you require further details on the expected timeline for this, please open a support case.