Correct, I think. But: your screenshots show the downlink ACK is using port 0?
That sounds good to me, as your screenshot also shows it's only a
DevStatusReq MAC command, without any application data:
4.3.2 Port field (FPort)
If the frame payload field is not empty, the port field must be present. If present, an
FPort value of 0 indicates that the
FRMPayload contains MAC commands only; see Chapter 4.4 for a list of valid MAC commands.
FPort values 1..223 (0x01..0xDF) are application-specific.
Now, I don't know if a
DevStatusReq is to be expected... (Maybe related to ADR?)
Is your gateway registered in TTN Console? If yes: what does the gateway claim is the content of the downlink? (See the "traffic" page for the gateway, on which you can get the binary data.)
The OTAA Join Accept will tell your node that it should use SF9 for RX2, not SF12. If the module is using SF12 in RX2, then the module is doing something wrong. If it uses an RN2483: you need at least firmware version 1.0.1.
However, it seems the ACK is received in RX1? If true, then that uses the same frequency and SF that was used in the uplink. Your screenshot shows the uplink is using SF12. So: all fine, if received in RX1.
Are you developing that RAK811 module? Then maybe you need to get in touch with TTN for commercial support. They'll also understand the specifications much better.