The wrong URL was given above; fixed now. Also, I added some details from Slack to @mvdswaluw’s post.
What happened when you restarted Node-RED?
Same issue here. No data via MQTT since yesterday… Could you please share the new format of uplink messages if this has changed ?
The changes have already been documented in the quotes from Slack above. (The format has not changed, but subscriptions to /up/<some single field name> are no longer getting data.)
How are you subscribing? Also, as per @kersing’s suggestion: did you try to restart whatever software you’re using to subscribe to the MQTT data?
Restarting Node-Red did not solve the problem.
And (as asked as well) how are you subscribing? What is the subscription string?
My solution:
mosquitto_sub -h eu.thethings.network -t ‘+/devices/+/#’ -u ‘draxxxxxxxxxxx’ -P ‘ttn-account-v2.lxVC4Xpxxxxxxxxxxxxx’ –v (without up)
and a lot of grep;cat and cut
@arjanvanb Thank you. I do not have an account to the Slackworkspace, is there any information what “temporarily” means? I’d need my field values back 
Is it planned to activate field values again or is there another way of getting them?
I restarted again (using openHAB MQTT client) - still no values by subscribing to:
<AppID>/devices/<DevID>/up/<single field>:state:default
The fields have been enabled again according to messages on slack.
Could you try with “-t ‘#’” and no grep/cat/cut just to check if data is arriving? I’ve got mosquitto_sub running using that topic for well over a year without problems (apart from some back-end downtime) and am currently receiving data.
In a Node-Red node, you don’t give a connection string. In a number of fields you give the Access Key, Device ID and the corresponding field. As with MQTT it doesn’t work if you fill in a field. An empty field gives you all the information you need. So for now the problem is clear… Must change my Node-Red.
What you need to specify depends on the Node-Red node you are using. Are you using an MQTT node or the TTN Node?
I’m using the TTN node. But with some adjustments in Node-Red the problem is solved.
Care to share those adjustments for other users who might run into the same problem?
I use Node-Red to send data from my end-node to Domoticz. In this case Temp, Humidity and Pressure. Previously TTN sent this data per field but now it spits all data at once. Previously I had to collect all the data that came in randomly and only then send it to Domoticz. Now I get the data in a fixed format and only need to convert it to the correct format for Domoticz. That’s all 
Is there a mailinglist where outages like this one are communicated? If not, there should be one…
Thank. you, I just rebooted my client again but still get no field values. Seems the syntax has changed then?
Edit: just found that fields are disabled for performance reasons… 
Same problem here. I used to be able to get temperature and humidity readings with (e.g.):
mosquitto_sub -h eu.thethings.network -p 1883 -u '[application name]' -P 'ttn-account-xxxxx' -t '[application name]]/devices/[device]/up/temperature'
Since a couple of days this stopped working. I still get the full message with all the metadata by subbing:
mosquitto_sub -h eu.thethings.network -p 1883 -u '[application name]' -P 'ttn-account-xxxxx' -t '[application name]]/devices/[device]/up'
but I really just care about the payload… do we know when the feature will return or if there is a workaround? It’s difficult in my setup to process the full message.