Inconsistency using UDP with two ESP8266's

Thank you Noiasca, yes I intend to set different IP's for all the Slaves but for now I am only testing with one Master and one Slave at a time.

I'm sorry, I don't understand your comment about the gateway and the AP but I will follow it up and do some more reading to try to clarify it. Thank you for the pointer.

Re your request for a schematic, maybe the attached document that I use to track the IP's and numbers used will help?

Also, thank you for the link to the AP Class documentation.