I have an LG G7+ and this method worked for me on the first try:
- Disable Wi-Fi
- Enable Airplane mode.
- Go to Settings > General > Apps & Notifications > App info.
- tap 3-dots icon (upper-right).
- tap Show System.
- tap com.lge.ims.rcsprovider.
- tap Force Stop.
- tap Storage.
- tap each...
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