There is an option of the melt mod in the last tab that let you use the melt ability even when the tool is not selected, could you please check if you enable that and see if it works better if you disable it? Could you also make sure that you did not make a local copy of the mod and that you are using the one from the workshop (if you have a local copy you can just delete it)?

im more confused why thats an option

Well melting without the tool is an option because players may want to bind the melt action to another button and be able to use it any time, like a permanent ability of their character ;)