After a few weeks of being Standard legal, Leyline of Resonance, from Duskmourn: House of Horrors (see "'Duskmourn: House of Horrors'"), has been banned in MTG Arena Standard Best-of-One Constructed formats. It is also suspended in MTG Arena Best-of-One and Best-of-Three Constructed formats. However, this card is still legal in Traditional Standard (Best-of-Three), Limited formats (Draft/Sealed), or special formats online.
WotC designers' rationale for banning the card was that the Leyline of Resonance created a situation where games were non-interactive as concessions would happen on the first few turns of play. In a one-of-one online format, this makes for very unfun and quick games. They also made note that this is an issue that they believe to be unique to these specific online formats, and that the banning is "not based on the overall health of the Standard format."
As to whether or not this card may end up getting banned in IRL Standard, it is yet to be seen. The Gruul Aggro deck utilizes the Leyline, and it is currently sitting at about 15% to 19% of the decks in the Standard metagame. With the Magic World Championships this week, it is unlikely WotC will change anything about Standard until after that event has concluded, but it's not a bad idea to keep an eye on that event to see what the pros do with the Leyline.