It is not possible to determine the exact cause of the problem without further investigation, as all three claims could potentially contribute to the issue. However, the most likely cause of the reduced production of liquid oxygen would be Claim 1, as frozen water in tank 2 could block the flow of oxygen into tank 3 and decrease the amount of liquid oxygen produced. Claim 2 and Claim 3 may also contribute to the problem, but they are less likely to be the primary cause.