Yes I am on Android as well.
New “event” this morning: my JQ-300 was off (no LED). I unplugged/replug it, but the green LED is blinking again and again. Seems it cannot connect to the server.
Is it the beginning of the end for this sensor ? 
Android 
I’m using iPhone. Anyway, since this issue is server side, client app cannot fix it.
At some forums there are tries to install a custom firmware, for example here: Air quality sensor JQ-300 request · Issue #1644 · xoseperez/espurna · GitHub
But it seems is not ready at this moment…
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I dont use it right now, but if you need to check anything, just let me know what exactly. Connecting it is a matter of minutes.
No idea where I can find that device number, there is nothing on device itself.
Still the same problem and no answer from my email sent to [email protected].
This is very sad 
I was just starting to be have some graphs to analyze my home air quality (I find the graphs from the app too “slow” with this 2 hours samping rate + averaging).
Are some of you recovered to a working situation (for those who lost their MQTT/humidity values) ?
Hi. when will be available to add a second device. I have 5 devices jq300. I tried first with 2 devices, in the app work perfect but in HA, only work 2 devices few seconds, then only one works
I just received a JQ-200 yesterday. Initially I was having the issue where it was showing readings at start up then becoming unavailable. After reading this thread I thought I may have the same problem as a lot of people seem to have. It turned out that I just hadn’t managed to get it to connect to the wi fi properly. They seem to be very fussy about the network environment. I had to turn all the 5g networks and access points in my house off and have my phone and the JQ directly connected to my main router on 2.4ghz wifi. It still wouldnt work using the first method (green light) with either android or iphone but was able to use @icaballero 's method with iphone and now I have all sensors updating data regularly! 
Yes, I had to do the same (turning off the 5GHz Wifi to have only 2.4GHz network) so that I can link the JQ300.
However, after that I re-enabled the 5GHz and it was still working fine, until next power shutdown. The JQ300 cannot reconnect and I had to return off the 5GHz.
Did you also re-enabled the 5GHz or are you staying on 2.4GHz only (which would be a pity) ?
New version of the perthings app for Android. This has going worse:
- Now some of the interface appears in German (I don’t know why, I’m Spanish)
- Now it does not appear any data. Nor the live, nor the historic.It is connected, but no data.
- At least the problems to reset and connect the device to the network have been fixed…
I re enabled 5GHz but haven’t had a power shutdown yet so haven’t been able to test that. Will give it a try this week.
Solution may be to set up a 2.4GHz guest wifi with a different name and connect the JQ to that…
Think useful information for someone:
I had a device malfunction yesterday. After losing power, it itself did not connect to the network. Today I tried to reconnect it by re-adding it to the application, but in the application the values were unchanged, and in the integration it was available for 30 seconds, after which it became unavailable (I did NOT reboot HA all this time).
I even downloaded the latest version of the application — nothing helped.
In the end, I left everything as it is in the hope that then somehow it will fix itself. And after 5–10 minutes, I noticed that in the integration the sensors became available and the values began to change. At the same time, in the official application, the device is listed online, but does not show any sensor values.
Lucky you. I can left it connected/disconnected for several hours/days and nothing changes.
The app does not show nothing, the HA integration neither. I tried to remove from the app, add it again, reset, while the integration is enabled/disabled, etc.
I understood that for affected devices we get correct values when setting everything up (start of Homeassistant).
Would a workaround where we go through the whole initialisation phase for every update work?
Alas, in this case we will get a high probability of being banned. Previously, the integration constantly received data exactly along the path that is used during initialization. About a month later, the owners of the cloud began to block the IP addresses from which such requests came. As a workaround, I then delayed 10 minutes between updates.
The other day I released version 0.9.1. Try to run it. There is a chance that this will help to receive data from devices.
Question: Are you sure that the data received during initialization is really fresh? That is, the data is being updated.
I just thought that it is possible to make such logic that if the sensors are not available, then the integration will try to get data every 10 minutes by the method, as during initialization.
But it won’t make sense if the data is not updated.
And then the question will arise, what to do with the status of inaccessibility.
Thanks for your reply and your explanation.
I tried the newest version but sadly no luck 
same behaviour as before.
From what I can judge, data shown in the first 30 seconds seem to be realistic.
Maybe instead of a logic just use a parameter (alternative mode or something) to make things easier.
Trying to get it working again, I went into the official app and no device came out.
I re-paired the JQ-300, rebooted the HA and the sensors stopped being available, then removed the integration and rebooted, and reinstalled, but no sensor came out. I get the integration, but it doesn’t show any sensor.
The version of the app 3.3.9 does not show any value, instead version 1.4.1 shows the values and they are updated.
Are you saying that downgrading to 1.4.1 shows the real-time values in the app again?
Exactly, as the PlayStore version did not show any data, I have the .apk 1.4.1, I tried with this version and it shows the data, and if you enter from time to time the values are different. Displays all data except humidity.
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