dexcom delay on watch

I have my Dexcom sensor talking to my iPhone, and that has always worked well. A little over a month ago, I started using an Apple watch, and was delighted at how well that worked with the sensor and phone.

But with the update to iOS 15.4.1 and/or Watch OS 8.5.1 (the two devices updated within a few hours of each other) the display on the watch lags the display on the phone, and sometimes doesn't update at all. That is, sometimes when I try to view my Dexcom readout on the watch, I just see a line of dashes ("- - -") indicating lack of data. Sometimes I see a value (e.g., "117"). In either case, if I tap on the Dexcom value for the full graph display, then I see an updated value.

I've gotten into the habit of checking in this way, but it's irritating, given how well this worked a week or so ago. I don't know if this is a problem with the software/OS on the iPhone (unlikely) or with the OS on the phone (much more likely), but I'd like to know who to talk to in order to get this fixed!