What to do with scaling issues of subscriptions?
Prisma 1 supports realtime subscriptions out-of-the-box. With a high amount of parallel subscriptions, Prisma's subcriptions sometimes become unreliable. This is a limitation of Prisma 1 that will not be resolved. Instead, Prisma 2.0 will eventually have a robust and scalable event system that enables similar funcionality as subscriptions in Prisma 1.
If subscriptions are critical to your application and you regularly experience heavy load that makes subscriptions unreliable, there are alternatives to Prisma such as Hasura with GraphQL subscription support.