@Solla-topee 

Hello,

below you can see answers.

1. Hello, can you show me a screenshot of the "Welcome to TP-link AC1900" after the firmware update? 

2. Is there any other modem or router in your network that is AC1900? 
No, no other router or modem in my network.

3. Except for the "Welcome to TP-link AC1900" and device information missing, is the router still running and you still have internet access?

Yes, router running and network connections work, but sometimes network not works and i need to wait couple minutes to work again. I tried reboot router but this not solve my problem.

Also strange is that all LEDs on router blinking at once (reboot not help).

I wanted to perform factory reset from "Backup and restore" but after click on button nothing happened also backup setting button not works. After all options i tried last one which help me. I performed HARD reset with button in back of router i push it for few second (help me after second attemp) now everyhing works fine. I have "Welcome to TP-link AC1200" back also all information show correctly and LED now work fine. Maybe it will help someone.

Thank you for your help and time.

@Solla-topee 

Hello

I had the same problem.

The gordonix solution seems to work, but in my case I had to perform a "hard reset" at least 6 times to solve this problem.

Is there any chance for someone to look at what caused this situation so that it does not happen again in next update? Or is it an already known bug?

Thank you in advance for your answer.