Answer by taking a quote from the following article:

From First to Last is an American post-hardcore band based in Los Angeles Area and Tampa, Florida. The current line-up consists of lead vocalist and multi-instrumentalist Sonny Moore, lead guitarist Matt Good, rhythm guitarist Travis Richter, bassist Matt Manning, and drummer Derek Bloom. The band released their first EP titled Aesthetic in 2003 which they recorded with founding member and vocalist Phillip Reardon who left the band in 2004 due to personal and creative differences. Dear Diary,

On July 30, 2016, former vocalist Sonny Moore held a radio show on Beats 1 as Skrillex, a link to which From First to Last shared on their Facebook page. The final song of the radio show, a "Bonus Track" was played and sounded reminiscent of prior From First to Last work with Moore's vocals, but had a lyric referencing SnapChat, indicating that the song was likely new. An Alternative Press article regarding a possible reunion with Moore and the band was also shared on From First to Last's Facebook page.  On August 1, 2016, Spencer Sotelo announced on Twitter that he no longer considers himself a member of the band. He also hinted that Sonny Moore is going to reunite with the band.  On January 15, 2017, the band released a new single, "Make War", featuring vocalist Sonny Moore and original drummer Derek Bloom returning to the band (Although in the single it was actually recorded by Blink-182's drummer, Travis Barker as noted by their Instagram.) Their first show back with Moore and Bloom was on February 7, during an Emo Night event in Los Angeles, California. This marked the band's first live performance with Moore in ten years and Bloom since his departure in 2010. Longtime bassist Matt Manning also appeared with the band during the show; having only performed alongside Moore briefly before his initial departure from the band. Aside from debuting "Make War" live, the band played a set featuring material strictly off of Dear Diary... The show was live streamed on Skrillex's instagram account. It is unknown if this was a one off performance or the first of many for the band. Guitarist Taylor Larson was not present at the performance, and is no longer a member of the band.  In 2017, Moore stated that "Make War" was the first song that came out quick. He later stated that the band plans to release more music.  In December 2017, the band released a new song entitled "Surrender" at L.A's emo night. This makes the first single with all members from the "Sonny" era (no guest drummers, etc.).

Did the Bonus Track ever wind up on an album?
indicating that the song was likely new. An Alternative Press article regarding a possible reunion with Moore and the band was also shared on From First to Last's Facebook page.