Scheduling keeps getting turned off

Every so often, without any notice, the plugin stops putting out tweets. I don’t notice it, since there is no warning, and end up checking it and seeing that it has stopped, then I press “Start sharing” again, and away it goes.

I don’t know how long it is, typically, before it stops, so I can’t check it on a regular basis, to minimize the non-working periods. Of course, that shouldn’t be necessary anyway.

Why does it stop? How can I prevent it from doing so? Thank you.