nHapi returns error for valid HL7 files while doing validation concurrently

[v-nmadwani]

We are using nHapi to validate batch of 1000 HL7 files (want to use it for much more files).
We are using Parallel.ForEachAsync loop with degree of parallelism set to 250.
For some of the valid HL7 files we receive errors as below:

1. An item with the same key has already been added. Key: ^~&
2. Index was outside the bounds of the array.Exception: System.IndexOutOfRangeException: Index was outside the bounds of the array
3. Operations that change non-concurrent collections must have exclusive access. A concurrent update was performed on this collection and corrupted its state. The collection's state is no longer correct.

Please suggest on this, we are kind of blocked on this.

Thanks