No event for token warnings logged when under high load

[bert-laverman]

During high loads, it is possible to get WARNINGs logged containing:

Caused by: io.grpc.StatusRuntimeException: CANCELLED: No event for token <some number>

This appears to be caused by a race condition where a transaction is confirmed before the previous transaction. In this case, the event stream from the client is canceled and reopened, after which all is back to normal.