@dmk 

No haven't tried in AP mode as not an operation mode that I need it to work in. 

I'm suspecting this issue is either a failing hardware component (e.g. the C9's power supply or something overheating at times) or a crash in the software e.g. Failing to deal with something in ios14 as I think this is when problems started on my C9.

I may try put all ios 14 devices only on my old router's wifi.

I tryied pulling over iOS/ipadOS 14 devices - dosen't change anything (this happens also when I'm away - I can see it in the logs).

I replaced also power unit with 3 different power adapters (12V + 2A+). No success.

Dying component in same time for so many users? I don't think so. Not that close in time...

Polish support replied, that they can't replace router with another model with same parameters and forwarde me to seller. What has reseller to do with warrenty/support problems of tplink? Of course seller don't want return my money, and I'm not suprised by that.

I'm preparing description of this thing for reddit and polish portal to warn any potential customars about how bad is tplink support and their products.

In my opinien they should do anything to pretend, that they are taken over by this issue. By they are not. I give them choice, and they made choice. So customers also should do the choice knowing, that buying high-end router from that company (or any other product) could cause serious time waste by warrenty support that are not working at all, asking same questions many times, providing beta firmware that are not working and voiding warranty.

To sum up - tommorow I will look forward to replace whole infrastructure by another company products. When this happen, I will comment everywhere to NOT buy tplink products, as they are provided "as is" and may work, may not work without support.

Srsly shame on you tplink and your "senior engineers".

My C9 is suffering from the restarting issue as well and it's driving me mad. The worst part is that the restarts are random so you always need to wait for hours between testing different potential solutions. I'm very close to returning my product and switching to another brand.

My setup:

- Archer C9 connected to a fiber modem using an ethernet cable

- No devices connected to C9 via cables, several devices connected via wifi

Things I've tried so far (without success)

- Calling the ISP to verify the problem is not on their end

- Switching the ethernet cable

- Switching to another power outlet (tried 3 so far)

- Updating firmware

- Disabling LED control

- Swapping the router to a new one at a local store. That's right - even this didn't help!

@Kevin_Z 

I tried everything and also with your support. For 2 days ago I changed the power settings to medium under advanced/wireless. I have not had a restart of the router since the, 22nd of October 20:40 until today. It has never been this long since the issues started.  Can this be something for you to look into?

Finally, I probably found source of the problem (no restart for last 3 days with intensive LAN and WLAN usage, TimeCapsule backups and more).

Of course I'm not going to publish source of problem and solution here, because support of tplink did exactly nothing to help me. Polish support at the end forwarded me to reseller (that's crazy - device is under warranty). Global support offered to replace unit with other model, but when I described what I need from this device (what is in specification of C9) they not respondend for few days.

Summary: DO NOT EVER BUY TPLINK AGAIN. They have no idea what's going on, what is source of the problem and how to resolve it. They are doing everything to close firmware, and also everything to stop updating firmware as soon as they sell all devices leaving customers without any support.

My D7 suffered from same issue few years ago and I was debugging for weeks what's going on - support also didn't helped then. And I found bug. And after about 1.5 year they released upgraded firmware with fix. Yeah, about 18 mounths later.

So don't be stupid - don't trust this company anymore.

So I have had the same issue for the last 2-3 weeks. I disconnected my iPhone from the Wifi and lo and behold, for 2 straight days I have not had any issues. Tonight I reconnected my iPhone to the router, and 1h later the router suddenly restarts itself (as it has been doing daily for the last weeks). I'll try this out some more but I'm starting to suspect there is something with an iOS update which is bugging out the router when the iPhone is connected to the wifi. Will try both 2.4Ghz and 5Ghz connections to see if there is any difference there as well.