hmm, foxed by this. ???
Looked in my wildflower book, given the height and leaf description here are those that fit (some you've probably discounted already)
a form of wild rose, or raspberry, wild mullein, meadowsweet, canadian fleabane(conyza canadensis), hawkweed(hieracium umbellatum), prickly sow-thistle(sonchus asper), bristly ox-tongue(sonchus oleraceus), great lettuce(latuca virosa), great willowherb(epilobium hirsutum), rosebay willowherb(chamaenerion angustifolium) himalayan balsam(impatiens glandulifera), hemp agrimony(eupatorium cannabinum), - and if it's none of the above I'll be out of ideas! ??? :-\
Let us know if it looks anything of the above.
Ask your fellow plot-holders?