Forum Discussion
Queueing of multiple actions prior to routing (before the interaction is initiated and before the sim heads toward the object) results in multitasking of incompatible actions such as "use toilet" and "shower". This causes cancellation of the second task since the sim attempts to interact with the second object before beginning the first task.
This was nicknamed the "toilet bug." It should have been fixed in the last patch. It was for most of us. Is it still happening for you? Do you have mods or CC? If so, remove them and see if you still have the problem.
Also, there is a second bug where having a baby or bassinet near the shower (it doesn't have to be in the same room) will cause Sims to cancel the shower action prematurely. Moving the baby further away or aging the baby up usually gets around this problem.