Was the one-time payment for a level or a custom capability?
I ask because subscriptions are only for levels, and the user buys a different level, the subscription for the one he had gets cancelled.
I don’t think that this should happen when it’s just the purchase of a custom capability without the level.
Could you show me the shortcode for the form/button the user got when he paid the one-time and got his subscription cancelled?
I look forward to your update.