I am having this same issue, but as OP mentioned, other subscriptions are just fine. It's very odd..
For instance....
2 months ago I spun up a couple PoC licenses (2-BizPrem 1-E3) and an Azure Free Trial Subscription. No issues whatsoever.
This PoC environment was supposed to be the only one before production stages, but, things. Spun up a second set of same licenses.
Now, MS is good, when I tried to do a Free Trial Subscription again, forced me into Pay-As-You-Go (likely because it very much knew through various methods I was me again).
But still, no problems..
Now, my client is ready for production stages on a tenant that is fairly older but never had an Azure subscription. PoC environments were base-level resources for the skeleton, and now production environment is supposed to be a bit more robust.
When attempting to create VMs in pretty much any "reasonable" region, I receive the same error (... NotAvailableForSubscription). I can't even create the default base size 2vcpu 8gib
BUT
My PoC version 2 environment, created last month, and following the exact same layout, settings, resources, etc... with an already active VM.... can not only create another default base size, but when choosing a different size, has complete access to pretty much - everything...
Quotas between the two all line up perfectly (aside from what's used in PoC shows up as used in quota) but limitation are all the same...
WTH is going on?