Currently none of the existing methods for determining log space free give a true value when using vCore. With vCore you are allotted a fix amount of space for your logs when you set the storage size. For example, if you specify 1TB of storage, you get 300GB allocated for log. However, if you run something like DBCC SQLPERF(LOGSPACE) you will see the Log Size (MB) and Log Space Used (%) values fluctuate wildly. The Log Size value may say 4947 (4MB) but the Log Space Used shows 99.92%. This leads you to believe that your 300GB of log space is almost full, when in reality it is that the currently allocated space is full and the log file would grow soon. This is of course an assumption since I can't find anything that defines it in detail. I've also put in a ticket with Azure support and was told there was nothing that would tell us this info, that we had to put in a ticket and ask them each time.