VAT are randomly not applied

The rules seem to be not invoked for randomly without more informations for now.

Try to reproduce:
In anonymous (not logged), create new order, go to cart and proceed to checkout (use PayPal Express Checkout and validate the payment), it's good, all vat tax are correctly applied related to this country. Do not log out you and place a new order like previous step. During the checkout process (cart and step 1), vat tax is not applied and rules for vat calculation not invoked.

My configuration:
VAT FR (eu) 20%
VAT/Tax Rules overridden: no
commerce_kickstart: current stable
commerce_vat_eu: current stable
oauthconnector: current stable (I have tested without this, using "classical" login form, but same issue)
commerce_paypal: current stable

Edit: After hours of debug, the bug is related to commerce_paypal (express checkout) and not commerce_vat. The customer/user profile is probably altered after the payment have processed from PayPal EC.
My solution for now is to disable the "Update billing customer profiles with address information the customer enters at PayPal." option in PP EC.
Edit2: Another solution is to apply the patch from this node: https://www.drupal.org/node/2036929

Check the related issues.