I have a WP40 Louet which has similar issues. What I have found is that, depending of the type of yarn, putting less tension on the warp helps this issue. It appears to me that the construction design of my WP40 as a rising shed loom, does not adjust enough for this. ie, with counterbalance looms there is equal tension applied to the upper and lower sheds. On jack looms this does not happen, so most Jack looms compensate for this by having the warp dip in the middle which sort of creates a fix. What I also did to my loom was to lower the harnesses a little to create this dip. It fixed it enough for me and allowed more tension to be applied. Hope that makes sense.
Jane does discuss this issue in Season 1 where she compares different looms etc.