The best thing I've done is after the vines are removed, is apply apply 12.5% and whatever soap you prefer,.. let it dwell for at least 30-45 minutes,..with re-applications at about every 10 minutes,..then hit them with the washer and many should come off. I don't normally recommend using that strong of SH on vinyl,..but sometimes with issues such as these "suckers" from vines there's not much other choice. other them to leave them on. If you have a hot machine that may work also to soften them,..but not to hot,..may warp the siding.
Don't feel bad these can be tough. They actually release from painted surfaces better than vinyl,..paint isn't as porous as vinyl.
Do these at the start of the job and by the time the job is done they should be softened considerably.
Jeff