Wifi Syncing Error (1 file failed / no wifi connection available)

A few days ago I noticed that my watch began to fail syncing over Wifi. When I choose Sync from Control center with wifi enabled (and phone is disabled) it starts syncing but in 3 seconds says 'No app or Wi-fi connection available'. When I go to Settings > Connectivity > Wifi and click Sync there, it also starts syncing and in 5 sec says 'Transfer complete (1 file failed)'. See the step-by-step screenshots below.

What I have already tried:

  1. Soft reset ('light' button for ~15 sec, then wait ~30 sec, then start the watch).
  2. Updating to the latest firmware (20.29 to 20.31), then soft reset.
  3. Connecting to PC with cabel and syncing over Garmin Express. Then soft reset.

On each of attempts I've received the same outcome as displayed below on the screenshots. In the meanwhile, syncing via Garmin Connect app on iOS works fine, no errors.

I don't use wifi syncing often, so it's not a big problem for me. But it's a bit diasppointing, because I prefer my fresh new watch to work stable, with no problems.

Is it a common issue and what is the solution? I found only one post on this topic (see item 3 above), but it did not help.

Syncing from Control center:

Syncing from the Settings: