Common problem with some hulls.My CCP did this all the time.My 210 WAC, not much.Work around is not hard, especially with a two person crew.Load up just like you described above. Now pull forward a few feet and crank up the slack. You may find that you need to do this several times on certain occasions. Less on others. Somewhat of a PITA but a solution that requires no additional work on the trailer (my opinion on why this happens). Did this for 14 years without mishap on my CCP so.....Next time out give it a try and see if this is acceptable to you. It will definitely get and keep the bow on the roller.Good luck.
No more single strap for me.