I've always used the fat boba straws to stack my cakes but recently ordered some that are not as stiff/strong as what I normally buy. Does anyone know if this is an issue ? Don't want any cake catastrophes! Thanks in advance.

It would depend on the size of the cake.  Plastic drink straws are usually very strong.  Stand several up straight and push down on them.  You will find they donot bend (or they should not!)  I use McDonald's (restaurant) straws.  If you can get your hands on at least one of those you can compare it to what you bought.

The hollow cylinder is always strong, even when the walls aren't that thick.  If you cut a length and try to crush it from end to end between two books, I doubt that you can make it bend or crumple.  You should be just fine.

Thank you both much appreciated.