destination ip=<ESP IP addr>, destination port=8888, source ip=<Linux IP addr>, source port=57907
The ESP UDP test uses the following values when it responds with "acknowledge". Note the destination port is the remote/source port.
destination ip=<Linux IP addr>, destination port=57907, source ip=<ESP IP addr>, source port=8888
Perhaps the terminal program sends to port 8888 and expects responses on port 8888. But it should listen for responses on the source port it sends.