Anker is recalling a power bank model: the 535 (PowerCore 20K) A1366. In some cases, the devices can overheat and start a fire.
If you own such a model, Anker advises you to stop using it and to dispose of it at a recycler. If you are not sure which model you have exactly, you can find on this support page a few further notes.
You can then also request a refund for the purchase amount on this page.
Problems can always arise with devices with modern batteries. Ideally, you should not charge any devices unattended or overnight. In cases where there are defective series, it is always good if the company initiates a recall. It’s best to spread the word to people who own one of these models but aren’t necessarily enthusiastic enough about the technology to know about this recall.