MutateIn modifies global Transcoder setting, possibly corrupting data for all other operations.

CouchbaseCollection.MutateInAsync does the following to copy Serializer from per-operation options.

if (mutation.Transcoder != null && options.SerializerValue != null)

{

    mutation.Transcoder.Serializer = options.SerializerValue!;

} 

However, mutation.Transcoder may be a reference to the Singleton-registered OperationConfigurator.JsonTranscoder.  So if a call to MutateIn specifies a custom ITypeSerializer in the options, then all future mutation operations will use that ITypeSerializer.

The core of the problem is that nothing registered as a Singleton should be mutable in the first place.