A number of issues can produce intermittently slow Internet access, and most of them don’t involve foul play. You could have bad cables, a bad modem or router, or outdated firmware on either of these devices. But as much as we’d like to think otherwise, your problem could be with a dishonest neighbor. Use a long, random string of numbers, upper- and lower-case letters, and punctuation, and avoid anything found in the dictionary. In addition to your password, make sure your Wi-Fi security is properly set up.”]
Source: https://www.csoonline.com/article/2134320/how-to-keep-your-neighbors-from-hijacking-your-wi-fi.html