Hi Watchpilot, sorry to hear about your problem, with the watch locking up (stopping) when you start the chronograph.
The IWC service center (or a competent watch maker) should be able to adjust the chronograph clutch so that the lockup doesn't happen more often than once every 100 to 200 chronograph uses, which should be ok for normal everyday use. I believe the underlying problem is inherent to the oscillating pinion clutch design of ETA/Valjoux 7750 derived movements (like the IWC 69000 series of movements), with pairs of teeth clashing once in a while when the clutch engages, and can not be completely avoided/adjusted away, but most people will not notice it at the 1/100 to 1/200 probability level.
I had the same problem with a brand new Portugieser Chronograph purchased in 2020. It would reproducibly lock up every 15 or so chronograph starts. After sending it to the Dallas service center twice, it would lock up on average every eight chronograph starts, so twice as often. The dealer inquired with IWC, and when IWC stated they considered the watch performance acceptable and would not do any more work on this problem, the dealer generously replaced the watch. It was a really frustrating experience, but with a good resolution.
The replacement watch (from 2021) originally had a 1 in 100 lockup rate. It has just come back from an IWC service (due to increasing rate irregularity), and locked up after 4, then 17 and then 57 more chronograph starts (1 in 25 average), so it seems it could be adjusted better, but I'm not going to bother sending it back right away. A 7750-based 3712 (Portugieser Rattrapante) locked up after 147 chronograph starts on my one and only trial, which is why I believe that a) the problem is inherent to the clutch design, and b) most people will not notice it on a watch with a well-adjusted clutch.
Best of luck with getting your problem solved, and please keep us posted here on the further developments.
