Same boat as those above. I have a 9 month-old 2019 Trek Madone SLR6. I ride only on tarmac 100-150 miles a week (but took a few months off during the lockdown) and twice in the past few weeks I’ve noticed that the seatmast is moving side to side. I stop on the side of the road and tighten the isospeed bolt which seems to solve the problem. Then I take it to the LBS for an inspection, just to be safe, ASAP. It’s frustrating, but so far nothing serious. Like some of the posters above I’m on the big end, 212 LBS, but well within Trek’s stated weight limits. Like them I’m wondering if the Madone isospeed isn’t clydesdale-friendly. My wife wants me under 200 LBS; now that the bike agrees with her it might be time for a diet. Anyway advice and info on how Trek responds to the issue welcome!