Entity Framework Core does not support multiple parallel operations being run on the same DbContext instance. This includes both parallel execution of async queries and any explicit concurrent use from multiple threads. Therefore, always await async calls immediately, or use separate DbContext instances for operations that execute in parallel.

When EF Core detects an attempt to use a DbContext instance concurrently, you'll see an InvalidOperationException with a message like this:

A second operation started on this context before a previous operation completed. This is usually caused by different threads using the same instance of DbContext, however instance members are not guaranteed to be thread safe.

When concurrent access goes undetected, it can result in undefined behavior, application crashes and data corruption.

https://docs.microsoft.com/en-us/ef/core/dbcontext-configuration/#avoiding-dbcontext-threading-issues