Hello everyone,
based on similar topics, I see that this is quite a common issue. I post it here just for information.
I have 1 Omnia and 2 MOXes and recently they started to notify me with this message:
Updater failed:
runtime: [string “requests”]:430: [string “utils”]:422: Unable to finish URI (https://repo.turris.cz/hbs/omnia/lists/pkglists/datacollect.lua): Download failed
I didn’t get to look at it in detail yet. First I’ll try to restart them 
I’m seeing similar problems. I’m not sure how long it happens, because I enabled e-mail notification only recently. In my case, the notification says:
runtime: [string “requests”]:430: [string “utils”]:422: Unable to finish URI (https://repo.turris.cz/hbs/omnia/lists/pkglists/openvpn.lua): Download failed
When I try to download the file manually via wget (from the router) it works.
The error is reported approximately once a day. Some days, there is no error, once, the error was reported twice a day. I guess, the updater is run periodically, however, from the message it’s not clear whether the failure happens in every run or only occasionally.
~~ File: /etc/os-release ~~
NAME="TurrisOS"
VERSION="5.2.0"
ID="turrisos"
ID_LIKE="lede openwrt"
PRETTY_NAME="TurrisOS 5.2.0"
VERSION_ID="5.2.0"
HOME_URL="https://www.turris.cz/"
BUG_URL="https://gitlab.labs.nic.cz/groups/turris/-/issues/"
SUPPORT_URL="https://www.turris.cz/support/"
BUILD_ID="e108301"
OPENWRT_BOARD="mvebu/cortexa9"
OPENWRT_ARCH="arm_cortex-a9_vfpv3-d16"
OPENWRT_TAINTS="busybox"
OPENWRT_DEVICE_MANUFACTURER="CZ.NIC"
OPENWRT_DEVICE_MANUFACTURER_URL="https://www.turris.cz/"
OPENWRT_DEVICE_PRODUCT="Turris Omnia"
OPENWRT_DEVICE_REVISION="v0"
OPENWRT_RELEASE="TurrisOS 5.2.0 e10830193c9377b0cb8788c9b22c4936d395fcc3"
Same here with latent Update
Ok, another Omnia in a different country does that, so 4 devices in total All updated.
reForis version: 1.0.7
Turris OS version: 5.2.0
Turris OS branch: HBS
Kernel version: 4.14.232
It happens to me as well…
Error notifications
===================
Updater failed:
runtime: [string "requests"]:430: [string "utils"]:420: Getting URI (https://repo.turris.cz/hbs/omnia/lists/pkglists/datacollect.lua) failed: Couldn't resolve host 'repo.turris.cz'
At my place once a day at different hours
runtime: [string "requests"]:430: [string "utils"]:420: Getting URI (https://repo.turris.cz/hbs/omnia/lists/pkglists/net_monitoring.lua) failed: Couldn't resolve host 'repo.turris.cz'
===
Edit: DNS no forward, activ DNSSEC
I have the same for several last days. Turris Mox, it is happening once a day after latest update.
We are experiencing a high load on our file server for some time. We are working on the move (in reality, we are testing a new instance already). That should help with random download failures (Download failed).
This seems like some other issue. The issue with load on our files server causes download failures but this is failure of DNS resolution. This is something in your local network or in router’s configuration. Verify that router has DNS correctly configured and working.
Every day I get notification
Oznámení o chybách
Updater selhal:
runtime: [string “requests”]:430: [string “utils”]:422: Unable to finish URI (https://repo.turris.cz/hbs/omnia/lists/pkglists/nas.lua): Download failed: Couldn’t resolve host ‘repo.turris.cz’
I can well resolve repo.turris.cz from Prague. 
I’m on Turris OS 5.2.7 and when I run updater manually form reForis, it seems to work well, i.e. no error.
In my case, the issue disappeared after uninstalling mwan3.