Leaning Cake!!

Hi everyone, I have been making cakes for 1.5 yrs now. I recently had an order for a 5 tier cake with each tier 5-6" tall. cake was 6"8"10"12"14" . first 3 tiers was stacked and was fine overnight. We stacked top 2 tiers on site. it looked slightly tilted but nothing horrible. well 6 hours later the cake was leaning a lot more, then another 5 hours and it was even more. what could have caused this? my dowels were actual higher than the cakes so the cakes were sitting on the dowels. I think I didn’t put enough dowels. Maybe I should have done waaay more. But it was up for a good 11 hours until they served it. (granted it was leaning)

the lady called and thanked me for the cake and loved flavor and design and of course height :) she thought it tilted cuz it was up for too long. I didn’t want to say no lady it’s cuz I didn’t dowel enough!

HAS THIS HAPPENED TO ANYONE? WHAT COULD BE THE CAUSE?

THANK YOU LOVELIES