Fasting & Menstruation
I have already watched this. This is about prohibition of fasting once periods have started. The question is different. The question is, if the periods start while a woman is fasting will the fast break?
If you’ve completed the last فرض of salah, then salah is complete.
Of course, if after salam your wudu invalidates then there’s no problem with your salat. I’m not sure what you mean by example of tawatur. Tawatur means that people today adopt a practice which has no evidence of being corrupted since it’s initiation. When validating tawatur we look for counter examples.