at NXT TakeOver: WarGames, in which the Undisputed Era lost to the team of Ciampa, Lee, Dominik Dijakovic, and Kevin Owens. The next night at Survivor Series, he then defeated SmackDown's Intercontinental Champion Shinsuke Nakamura and Raw's United States Champion A.J. Styles in an inter-brand triple threat match. On the December 25 episode of NXT, Strong would defeat Austin Theory to retain his NXT North American Title. At NXT Worlds Collide, Strong and the rest of The Undisputed Era would face Imperium but would lose the match. On the January 22, 2020 episode of NXT, Strong lost the North American Championship to Keith Lee in the main event, ending his reign at 126 days. Strong then began feuding with Dexter Lumis, who came to Velveteen Dream's aid to help him in his war with The Undisputed Era. During that time, Dexter kidnapped Strong during the In Your House event to keep him from interfering in Cole's match with Dream. Though returned to his allies, Strong was heavily traumatized by the kidnapping and developed a deathly fear of Dexter as a result. His teammates attempted to curtail his sudden panic and fear by having him go to therapy but his therapist was O'Reilly in disguise, due to Cole's paranoia that Strong might renounce villainy as a result of his encounter with Dexter. At The Great American Bash, Strong lost to Lumis in a strap match. In September, The Undisputed Era started a feud with Pat McAfee, Oney Lorcan, Danny Burch, and Pete Dunne, turning them face in the process. This culminated at NXT TakeOver: WarGames (2020) in a WarGames match with the Undisputed Era winning. At NXT TakeOver: Vengeance Day, Cole superkicked O'Reilly, leaving the future of the faction in uncertainty. On the February 24, 2021 episode of NXT, Cole turned on and double-crossed Strong, thus disbanding The Undisputed Era. After the dissolution of The Undisputed Era, Strong took time off from NXT. Diamond Mine (2021–present) Strong made his return on June 22 episode of NXT, attacking Kushida, as the Diamond Mine stable along with Tyler Rust (who was released weeks after and later replaced by The Creed Brothers and Ivy Nile) and Hachiman, with Malcolm Bivens as their manager, turning heel once again. On the September 21 episode of NXT 2.0, Strong defeated Kushida to win the NXT Cruiserweight Championship. At NXT WarGames, Strong defeated Joe Gacy, retaining his championship.