The conservation laws are statistical, at least to a degree. Local apparent violations can be OK, provided the system as a whole absolutely complies.
There's no question that if the claim was as appears that the conservation laws would be violated system-wide, which is a big no-no.
So we need to look for alternative explanations.
The most obvious one is that the results aren't being honestly presented, that there's so much wishful thinking that the researchers are forcing the facts to fit their theory. (A tendency so well known, that it's even been used as the basis for fictional detectives.)
Never trust results that are issued in a PR statement before a paper. But these days, it's increasingly concerning that you can't trust the journals.
The next possibility is an unconsidered source of propulsion. At the top of the atmosphere, there are a few candidates, but whether they'd impart enough energy is unclear to me.
The third possibility is that the rocket imparted more energy than considered, so the initial velocity was incorrectly given.
The fourth possibility is that Earth's gravity (which is non-uniform) is lower than given in the calculations, so the acceleration calculations are off.
When dealing with tiny quantities that can be swamped by experimental error, then you need to determine if it has been. At least, after you've determined there's a quantity to examine.
