The g36 has been in use for almost 20 years by countries all over the world. If there was a design flaw that manifested after firing only two magazines or when the temperature was 86F it would have been discovered immediately. It would also be easily replicated, but Lithuania tested the rifle and found no problems.
It’s pretty obviously a quality control problem, affecting individual rifles. Switching to a different type of rifle by the same manufacturer wouldn’t fix that sort of problem.