The way the 1769-AENTR is designed, it only waits two to three seconds after power-up to detect backplane communication with the modules on its rack. After this period, it makes no further attempts to detect modules on the rack.
The new operating system used with the 69E and 69L modules does not boot-up and load its driver stack in such a short timeframe. So the AENTR does not recognize these modules.
A workaround is available. In the Logix controller program, go into the module properties for the 1769-AENTR Ethernet adapter. On the Module Info tab there is a Reset Module button which will restart the AENTR. Since the 69E/69L module has already booted-up and loaded its backplane communications driver, the AENTR will then be able to detect it.