I have exactly the same problem with Forerunner 620
The Stride Length suddenly disappeared from my stats.
May 2 was OK
https://connect.garmin.com/modern/activity/1711295623
May 4 and 6 no data for stride length. I have sent an email to support as well
https://connect.garmin.com/modern/activity/1714863377
https://connect.garmin.com/modern/activity/1716641449
And why is it that people here, with different watches than our 235's, are complaining about the same subject??
Do you have a list of which models are affected and which one's aren't? Don't just assume it's affecting every model or even most models, as opposed to a minority.
Avg Stride Length is most certainly showing on my recent runs recorded on my FR630 (used in conjunction with a HRM4-Run chest strap with Running Dynamics support).
I have a FR235, but since I don't use it any more, right now I don't know if it's affected by this issue. Let's say I haven't seen any complaints about Avg Stride Length missing in the FR735XT and the FR935 sections of this forum.