It's possible the YN-E3-RT requires a TTL body to connect with. The same happens with the YN RF-602 and 603 mkI
I don't have any troubles firing my RF-602's from my 124G, M645 1000S, or RB67 using the adapters listed above. The RF-602's only have a center pin contact, so no need for TTL anything. I have also had no issues with my YN-622's, which are E-TTL.