Metallic flavors generally do not come from oxidation (which is what could happen if you leave the cyser in a container with too much headspace for too long). They can come from an interaction of the acids in apple juice and reactive metals. While stainless steel is mostly inert to the concentration of acid in apple juice, aluminum and regular steel or iron are not. Metallic tastes can also be a byproduct of some yeast autolysis, so if you have a lot of lees in your cyser, too, that could be the issue. It is also possible to get a slightly metallic flavor from sorbic acid at high enough concentrations, so if you treated your cyser with potassium sorbate - that could be the problem.
The yeasty flavors in your mead are undoubtedly from the yeast lees that you see in your bottles. Re-bottling, taking care to only rack off the clear mead and leave the lees behind, could solve that problem with time. But it will take some time for the yeast autolysis byproducts to age and mellow.