you don't want to over pot a hoya or any plant. the reason is that when you water the soil tends to stay wet too long causing fungus and root rot. I don't know what kind of soil you have it planted in but over the years it could have broken down and turned more "peaty" which holds even more water. So my best guess is that it is too wet and you need to repot in a well draining mix. gl (yes it is a hoya)