Apparently it's common if used with milk. I only use it for water and it's been good so far x
Yes we have before, we descarded the straw and bougjt replacements. We find washing the cup straight after milk and completely disasembling all parts (fold on lid, lid seal etc and using the tum tum official straw cleaners keeps them clean
It's happened to me with water I don't use it for milk. I do clean it regularly so found that odd. Guess I will just replace every few months
Just replace, mould can be so dangerous