time series looping ts_gnn_ seems to work differently than other looped time series
ts_gnn_ contains values for all historical hours, e.g. below a screenshout from day 7 solve in
ts_gnn_ also remembers calculated future values
whereas ts_cf_ contains only values in current tt_aggregate
All this can be fixed by clearing ts_gnn_ in periodic looping, but that did alter the value of objective function and I reverted that fix.