While leaving your applications open in the background might be beneficial, especially while multitasking on your iPhone, some of them can ultimately crash. There's a potential that any of your other applications or the device's operating system would be compromised as well if this happens. To exclude this as a possible reason, close all of your background programs and then reopen the Messenger app.

1. To force background programs to shut, swiftly double-tap the Home button to bring up the multitasking interface.

2. After that, swipe up on app windows to shut them.

Whether the applications are actively operating in the background or in standby, this shuts them. Restart your iPhone, then open the Messenger app again.