Some messaging apps have a default setting that deletes older messages from conversations that have more than 200 messages. When thousands of messages are restored, this setting can cause a lot of problems because it keeps trying to delete messages when you try to open the conversation. If you are restoring lots of messages, please disable this setting by opening the Preferences/Settings of the messaging app.
Some phones can take a lot of time to index and process newly created messages, especially if there are thousands of them. If you get a blank screen, or if the phone asks you to “Force Close” or “Wait,” just press “Wait” and leave the messaging app running. Eventually it will finish processing and start working normally.
If the messaging app opens but doesn’t show the newly restored messages then you may need to clear its storage from the Phone Settings > Installed Apps screen to force it to refresh the messages.