The crashing thing I think happens because of how WLM handles interacting with offline contacts with Escargot patches atm. That’s normal I suppose. As for the other issue of them not appearing online, you’ll have to log out and log back in (or get your contact to do the same).
Me and him have tried different techniques of Uninstalling Messenger and using different versions, But hes unable to see that im Online and some others apparently. Even thou to him it says he has added me as a Contact, On my end, it doesnt show him as an added contact on my list from the Settings > Privacy Area.