Repetitive failing attempts to update a router

Several users report about repetitive notifications from updater about failed update attempts. Although updater runs 6 times a day and the update/check for update is successful in the end, it's definitely an annoying matter that spams our users and generates unneeded traffic on our mailservers as well.

Also, the issue starts to be so frequent, that's at least suspicious for what's going on and what is causing this not so uncommon issue.

Last clues leads to failing repo.turris.cz domain name resolution and to Knot Resolver.

Some reports

• public forum:
  • Update Error On Turris 5.1.8
  • updater-failed
  • Problem s aktualizaci? - Updater failed
• internal support tickets
  • RT#1256943
  • RT#1261131
  • RT#1356544
• Several reports in comments below 👇 👇

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Original issue description

I have been getting the following error for the past two days when my Turris Omnia tries to update packages:

##### Error notifications #####
Updater failed: 

runtime: [string "requests"]:417: [string "utils"]:420: Getting URI (https://repo.turris.cz/hbs/omnia/lists/pkglists/luci_controls.lua) failed: Connection timed out after 60029 milliseconds