Dropbear high CPU load

Hi everyone!

I have switched from OpenWRT to LEDE recently on my two WR841 v8.4 devices and I encountered an issue with dropbear.

Recently I have built a custom LEDE built for one of my WR841 v8.4. I have included config files from previous OpenWRT installation. I have compiled succesfully an image, flashed it to the router, sysupgraded and rebooted. After reboot the device wih LEDE works like previously with OpenWRT, but I could not ssh into it. I connected to it via serial console and found out, that the dropbear uses almost 100% of CPU during my attempt to connect to it via ssh.
There is a line in logread

Sun Aug 20 14:17:29 2017 authpriv.info dropbear[1938]: Child connection from

and my ssh client on PC hangs for infinity without any message. This is just first of my WR841v8.4. I had (probably) the same issue previously on my second WR841.

I flashed custom LEDE to my second WR841 and there was the same problem. I did not troubleshoot the problem, just flashed OpenWRT via ftp/serial to it, then flashed stock 17.01.2 LEDE and then my custom LEDE build. After it the router did not respond to ssh request for about 20 minutes, but after that time I could connect to it via ssh and now everything is OK.

Build config used to compile custom LEDE image for my first WR841:
Version of LEDE used for build: r4700-364befeccf

My dropbear config is:

config dropbear
option PasswordAuth 'on'
option Port '22'
option Interface 'lan'

Has anyone any idea what causes this issue and how to fix it?

Problem does not occur in compiled custom image based on v17.01.2.