Absurdly high wrist-based HR AFTER activities since update 19.18

My 255 music has suddenly but consistently started giving me absurdly high HR wrist-based readings AFTER my runs. This suddenly started happening after the 19.18 update, and it now happens after every run.

Here's an example from today:

Details:

  • I use the HRM Pro chest strap during the runs. In the example, it measured an HR around 145 during the run.
  • After the run, when walking/standing, having switched back to wrist-based, the displayed HR rises to 230 and higher for some 5-10 minutes, until it seems to revert to something more plausible (in the meantime, the watch plausibly estimates my max HR at 190!).
  • If I switch the source to the HRM Pro, it shows a HR of around 90 (while the writst-based reading shows 230).
  • I have cleaned the sensor and rebooted the watch (repeatedly).
  • I can exclude this being due to the watch picking up walking cadence: it happens with and without walking.
  • Up until update 19.18, I had no issues whatsoever with the wrist-based HR.
  • I switched off source switching very shortly after the update (because I got bizarre back-and-forth jumps in readings at the beginning of runs).

Has anyone had similar issues? Any ideas what is happening here? Any help would be greatly appreciated.