Hoovering — named for the vacuum — is the attempt to suck you back into a relationship after distance or a breakup: sudden apologies, nostalgia, manufactured emergencies, gifts, or messages through other people. It usually spikes right when you're getting stronger. A hoover is a test of the exit, not proof of change.
Decide your response policy before it happens, while you're calm. If safety is a concern (threats of self-harm are used as leverage), you can alert someone close to them or emergency services — help arriving doesn't have to be you returning.