It does not only happens on CHR. But also on arm.
We have 3x RouterBOARD 1100Dx4 they are running 6.45.1
Two of them are heavily used and have 1000+ devices. They really constantly freeze in random time intervals - it can be a week or a month, but can be a day. The connectivity to winbox is lost, but it is possible to reach the board using mac-telnet and reboot it.
I think, that this behavior started after 6.40 version.
I have a RB1100AHx4DE that produced an error message when Winbox, Dude and TikAPP tried to connect, "connection refused".
SSH is ok and www webfig ok. No errors or events in the log except SSH and Webfig connections. I'd expect to see entries for the refused connections.
Firmware version 6.42.12 Stable with 35days uptime. Memory usage a bit high with 486MB free of 1024MB.
In Webfig I disabled the /ip/Winbox service then re-enabled it clearing the issue.