Physical Ethernet and BLE incompatibility?

[allabouttheip]

Hello.
I hope I am in the right place!
I have some code which continually sends a fixed length UDP packet over the internal physical ethernet at 1 packet per second. The packets contain a sequence number so I can track lost packets. Monitoring the output with wireshark the code runs indefinitely with all packets received in the correct order and with no losses. So far so good. With that code running as a FreeRTOS task I then enable NimBLE and implement a Nordic UART. Now just occasionally and sporadically a UDP packet will not be produced. The wireshark monitor skips a sequence number. But my UDP sending code does not return any error. Rather it just returns the correct number of bytes it has sent. But those bytes never appear on the wire. The Nimble uart doesn't need to be sending or receiving anything for this to occur. It is just sitting there advertising itself.
I have experimented with changing task priority levels, and pining the UDP task to either core, but the problem persists.
I appreciate its very difficult to help without seeing the code, but has anyone experienced something similar or can suggest any pointers as to where I might look?
The hardware is an Olimex ESP32. Code developed in ESP-IDF in Eclipse. FreeRTOs, LWIP, Netif.
Can anyone suggest anything please?
Thank you.