Apps keep unexpectedly uninstalling so they need to be reinstalled in order to use them

Hi, trying to resolve the problem of apps suddenly going dark (like they are when you are installing a program and it says waiting...) and being unable to be accessed unless they are installed again. This would be simply annoying if the phone was always connected to wifi, but it is using up cellular data like crazy and costing so much money. Tried uninstalling and reinstalling apps, but it doesn't help. Would appreciate some help and advice TIA