There are a couple of articles saying the Russians are experiencing up to 60% malfunction rates on some of their ordnance fired in Ukraine.
https://www.yahoo.com/news/many-60-russias-missile-strikes-114321086.html
I think the mistake made here is that a spent motor from a cargo rocket is misidentified for a complete rocktet with a HE warhead sticking into the ground. I've seen the remark/question pass on the Dutch ammo collectors site about this subject too.
The types of 300 mm rockets mostly used by the sowjets are the cluster ammunition and the thermobaric, both seperating the engine from the warhead.
It's also quite a confusing text with the picture; and unexploded tail section... which appears to contain cluster bombs.... I know the average russian ammo factory worker likes his wodka even on monday morning, but I assume that even in Russia a tail section containing cluster bombs would not make it through quality control.
Counting in these spent motors as duds will make the number of duds rise fast.
The article mixes up two different things. The US official would seem to be talking about guided weapons launched by complex weapon systems. For example the 9M79 and 9M723 series of ballistic missiles and cruise missiles such as the 3M-14 series, Kh-55 and Kh-101. The article then goes on to talk about an entirely different class of munitions, which it equates as being the same as those above.
The rocket motor bodies seen are mostly from the 220 mm unguided rockets of the 9K57 Uragan system, or the 300 mm guided rockets of the 9K58 Smerch system, along with 122 mm rockets from a multitude of different systems. Of the 11 common 220 mm rockets, only one is fitted with a unitary (HE-frag) warhead, all the others are dispensers (submunitions, mines, smoke, etc.). For the 25 known combat guided rockets of the Smerch, only two carry unitary warheads. Of the rest 18 are again dispensers, whilst five are separable unitary. I've not gone through all the 40 odd 122 mm models yet, but there's a more even mix of unitary and dispensers.
The rocket motor bodies seen are commonly not duds, but are just what's left of a rocket that was originally fitted with a dispenser or a separable unitary warhead. Once the payload has been dispensed/released, the rocket motor body, which is commonly still attached to the outer warhead assembly, continues to fly a ballistic trajectory until it strikes the ground. It is this rocket motor body, or combined rocket motor body/outer warhead assembly that is seen stuck in the ground.
Of course even unitary warhead equipped rockets/guided rockets, still have a rocket motor body attached to them and this will be found at or near the impact site, though they are generally in a far worse condition.
Many 'failed' bombs I've seen have been parts of crashes, shot down aircraft, likely dropped at the wrong height, or not fuzed correctly. I've not seen many that were obviously true duds (the fuzing system truly failed).
Even guided missile bodies of 9M79 and 9M723 series of ballistic missiles equipped dispensers warheads have been reported as duds. This is again incorrect. When the warhead operates and dispenses its payload, the now unstable remnant missile tumbles to the ground. The spent missile bodies, to those who are ignorant, are classed as duds. Unitary ballistic missiles, which either function correctly or have failed, will simply bury what's left on them in a steaming crater.
The final class I can think of are cruise missiles that have either been shot down, or have attacked a higher altitude target (radio tower, building etc.). Unless it's got obvious fragmentation or impact strikes on it from an external (not internal) source, then it's unlikely to have been shot down. If it had previously hit a high-level target, what is left will carry on relatively unimpeded until it impacts with the ground. If it buried itself into the ground and the warhead hasn't functioned, then the fuzing has failed, or wasn't fully armed at impact (many only fully arm when near their intended target).