By accident I found, that golioth uses a fixed retransmission timeout of 1s.
(I tried to upload a WireShark capture, but that seem not to work ;-).
The recommendation in RFC6347 is a backoff of 2, means on reach retransmission the timeout is doubled (see RFC6347 126.96.36.199. Especially with “narrow band” communication, the overall performance gets better with such a backoff strategy. E.g. with cellular NB-ioT the RTT is something about 2-3s and using fixed 1s retransmission results in a frequently useless retransmissions.