If you're currently not getting Helldivers 2 Medals for Major Orders then developer Arrowhead Game Studios is working on a complete overhaul of the rewards system amid reports of delayed and missing medal payouts.
In interactions over Discord, Helldivers 2 community manager Twinbeard has responded to complaints over missing Major Order medals, admitting the system has "been very slow or working on and off rather, for a long time." After responding to a number of players individually, acknowledging the issue, and pledging a rework of the system, Twinbeard issued the following statement summing up the situation:
"For those of you asking about outstanding medals: Medals for two of the latest three major orders have now been shipped. The last remaining batch will roll out in 16 hours (if Hammertime does its thing; if not, 11.00 AM CET April 10th). We will also do an overhaul in the future of the system handling these requests, as it's frankly about as reliable as a solar-powered watch in Malevelon Creek."
In one reply, Twinbeard clarified that it's the rewards system itself - and not the actual medals - that are being overhauled, so don't expect any immediate changes to the currency system. It sounds like the only thing being changed here is the delivery system, which will hopefully result in players receiving their medals for Major Orders within a reasonable timeframe.
The only real solution at the given moment is to simply wait, as it seems in the vast majority of cases the rewards will eventually show up. Thankfully, Arrowhead seems hard at work fixing the whole situation, but we don't know how long that'll take, with Twinbeard estimating the update could arrive "before Thursday or not I don't know," just in time for the Helldivers 2 Democratic Detonation Warbond.