It’s super common in group flights for one plane to end up like 100 NM or more ahead usually because of AP glitches, lag, or connection issues. Some pilots slow down if they are ahead or feel like there’s nothing they can do about the gap, but honestly, slowing down at that distance doesn’t really help.
If you’re the lead aircraft trying to bring the behind plane closer, try this - turn about 45° left or right off your route, and once you’re stable on that heading, just turn 45° back to rejoin the original path (you can also wait one or two mintues on the deviated heading depending on the distance). If you get ridiculously ahead like around 200 NM, a 360° circle works better.
Also, I’ve seen pilots try to overspeed in the trailing plane hoping to catch up that’s super risky and can give you a violation unnecessarily.
This is a really basic move, but I hardly ever see people doing it. It’s smooth, chill, and realistic. No messing with speed or altitude. Keeps your flights looking tight during formation events, screenshots, or scenic cruising.