I had some difficulty with the 900 series as well, but not nearly as much as yours show. The Old Copper in particular used to cake up and tended to flake off, especially as the jar got older. I lightly sanded pieces to try and even it out and compress the layers a bit, but towards the bottom of the jar that wasn't possible because of the flaking, even after adding some gum to the jar. I always loved the way this series looked but it was a challenge to brush on evenly and cleanly.
Nancy, the Old Copper is the glaze in the picture of the mugs that has huge curling and flaking (far left). I have some commercial glazes that are several years old and haven't had a problem with them adhering to bisqued pieces. I know the glazes haven't frozen while I've had them so I don't know what would have caused the gum to go. I don't have a lot of knowledge regarding glaze chemicals, but this is the first time I've experienced this problem.