The cache of tokens '_tokens' in servicebus' init.py is a global variable (dictionary). A token is created based on the request host, path, issuer and account key. But the key for the cache is only using the request host and path. So if you try to use 2 instances of ServiceBusService, with different credentials, the cache will eventually return tokens for the wrong issuer/account key.

The key cache 'wrap_scope' should include the issuer and account_key, or the cache '_tokens' needs to be a field of ServiceBusService instead of a global variable.