Yikes!!! That is odd. Hopefully it will finish leafing out so it can store up enough energy to survive winter. There are some pests and disease that attack althea so I’d look the bark over closely for any tiny holes that might indicate borers or other bark pests. Also check the base of the althea to make sure you haven’t buried mulch or dirt up against the bark. Brush any mulch or dirt away from the trunk until you find the original soil level where the trunk emerged from the soil in the pot or ball that it came in and keep it that way. Mulch or dirt piled against the bark slowly strangles the plant hindering and cutting off the flow of nutrients and moisture from the roots below to the stems and leaves above. This “volcano mulching” is an unfortunately popular and deadly trend lately. I see shrubs and trees suffering and dying from “volcano mulching” every day and it could cause symptoms such as this very late leaf out.