Extracted from 5.8 announcement topic:
RB-450G, after upgrade from 5.6 to 5.8 on all metarouters (4 metarouters running RouterOS, 32 MB RAM each):
execve: No such file or directory
Kernel panic - not syncing: Attempted to kill init!
CPU Usage of RB450g is about 40 %. The same happens even on freshly created new metarouter (fifth).
Downgrade to 5.6 helped. RB-450g has now 100 MB RAM free and CPU usage 1 %.
Are Metarouters in 5.8 broken?
I can confirm this. my 450G … 
Metarouter broken on RB493AH with version 5.8.
Broken on RB450G as well.
Are there any problems to revert to 5.6 ?
Error when connecting to console :
execve: No such file or directory
Kernel panic - not syncing: Attempted to kill init!
Yes they are dead! RB1100, RB450G, and RB493AH. That’s all I have tried.
not sure what RB1100 you tried but all PPC boards (with support of metarouter) worked fine, while any MIPSBE board failed to start RouterOS guest (OpenWRT worked)
It was our core router. It was something I was messing with a while ago and to be honest I couldn’t tell you when it broke. We actually had some metarouters die on AH boards and I remembered we had one on the 1100. When I checked it, it was also dead. But it is good to know they do work on PPC now. Thanks!
Hi, is openwrt now stable in 450G? Or does it keep randomly rebooting in this version as well?