Both of these are from RPi3 systems that got a fresh install with LE10 and are using the default skin. The non-working system, 'KodiLounge' got a restore of a config backup I took in 'KodiBedroom'. Turned on logging, did a reboot and played the same file on both boxes.
Here are the results from 'KodiLounge', where the amp did not pick up an EAC3 signal via HDMI
Here are the results from 'KodiBedroom', where the TV did detect it as a DD+ signal via HDMI.
Also on this box I'm offered 'TrueHD' and 'DTSHD' options in System/Audio settings (I'm not offered these on 'KodiLounge') which is more unexplained weirdness.