I’ve not seen re-transmission in any RAK devices. In general, not many devices do re-transmission due to the reason you gave plus the confirmation of messages can be very use case specific so a generic mechanism (like the one built in to the LoRaWAN spec) can quickly be redundant.
You could extend the firmware with the RUI compiler to resend if you don’t get a confirmation back, but with a different frame counter and something in the payload that indicates a resend - the network may well have received the message but the device may not have heard the confirmation.
Overall, it’s much better to just send and if the application server spots a gap, send a message asking for a re-send of a single or range of data points - most devices have enough memory to hold a few days worth. This is made even easier to implement if you have your own counter and leave the LoRaWAN frame counter for its original purpose of preventing replay attacks.
More help is possible if we have a little more detail.