Website Fast Tags support subscription apps (like Recharge) but might need some additional configuration. Please ensure the following criteria are met for a smooth fast tag / subscription integration.
Link Subscription SKUs and/or Variant Ids
If you use a separate SKU and/or Shopify Variant Id for subscription vs one-time items, make sure to create aliases for the subscription items as well.
Recurring Order Shipping Rates
Set up your subscription app to either recalculate shipping rates or always choose a standard (5+ day) shipping rate for recurring orders. If you're using the Recharge app, you should select Dynamic Shipping Rates. DO NOT select Retain.