As mentioned already, drivetrains wear together, if it is well worn, then replacing any one part can cause problems. This has always been true of all bikes, but it is particularly bad with half link chains because they really do stretch as well as wear (normal "chain stretch" is actually wear, but half link chain stretch can be both). Any good bike shop should have a chain "stretch" measuring tool for you to check your old/current chain.
Typically any half link chain will come up as needing replacement if you check it with this tool after just a few weeks of riding, that's how bad it is.
G.