Same thing happened to me, today I linked SIM1 and SIM2 phone and messages tiles and then unlinked them, after that SIM2 tile name was back again.
But there is one thing that has changed after that...
Before linking SIM1 and SIM2 messaging and phone tiles has same color. After unlinking SIM2 tiles changed color in to same color as it is inside sim2 aplication for phone and messaging. Now I can't find a way to change SIM2 tiles color.