Reply by PurpLev

if you jointed your cauls, but only clamped them at the ends – they could bow, leaving the center area un-clampped (by the cauls) which would then be free to move out of alignment, especially if you apply a lot of clamping pressure.

you should either make sure your cauls are convex properly and clamp on their ends, or if you use jointed cauls, make sure you clamp all along them.

-- ㊍ When in doubt - There is no doubt - Go the safer route.