Was wondering if anyone new about what to do if you flushed a soap bar down the toilet and if it could cause mold issues/smell or problems with the pipes? And what would you do?

If the soap bar isn't causing a flushing problem with the toilet, I would not worry about it at all. It will desolve just like it does in the shower or tub. If it is causing a problem with the toilet flushing, I would use a closet auger to break it up and send it down the drain. Otherwise no worries, okay?

A very brief answer -No.

Dad said it all, If the soap bar is causing a back up when flushing solids break nit up with a closet auger and send it on through, Good luck, Tom