spi.transaction.RequestTransactionManager is not thread safe

When running a s7 connection to an PLC sometimes the connection halts and this error is thrown in the log. It seems like the processWorklog function uses a thread safe queue but is itself not threadsafe throwing this error.

We're using an single connection to the plc. Reading two datablocks. Each datablock is read by a different handler running in a separate thread but using the same instance of PLC4J.