Yep. Standing start nerf from GT5P in action. Even without power shifting, the most advantage to be had with H-pattern was from a standing start, changing from 1st to 2nd, because this is typically the largest ratio gap in the whole 'box. So sequential users were waiting a lifetime for the revs to match, whereas we H-patterners were away like scolded cats...
It seems PD implemented a minimum delay timer (for 1st -> 2nd only) blocking the selection of 2nd if it's too soon after deselecting 1st. Just be more deliberate and slow before selecting second (i.e. deselect 1st, wait a fraction of a second, then select 2nd). You'll get the timing down eventually.