What did happen with RouterOS 6.21 ? It appeared on the web site, and later, it seems to be revoked.
Since it was revoked, there must be a serious issue affecting real-world installations. Why there is no urgent and timely mail with the description of the situation and recommendation of what to do ?
Really disappointed (not by possible bug, but by handling of this).
Who said it was revoked?
There was a 6.21 Thread. It had a serious bug.
On CCR1036 stable, but on x86 the equipment hangs, it very had bag
i find old package 6.7 work x86 stable
Long time know that mikrotik not test updates, always doing shit, we who are the idiots who ever tested for them.
Forgive me, it has already passed the threshold long time.
Trying to move the thread to something more constructive.
Does anybody have a reference or a description of the bug ?
What is affected ? Is it safe to try to downgrade ?
I’ll try to be more constructive, I will test not more.
If you read the other post you will know what I mean.
!NB! We have removed v6.21 from the download page due to upgrading issues from v5. Please use v6.20 until v6.22 is released early next week. We apologise for the inconvenience.
only using netinstall to resuscitate him.
I upgraded from 6.21rc to 6.22rc and the ccr got a kernel panic. i bootet the backup partition and recovered from that.
I used a handcrafted link to get 6.21, no issues so far.
When I have also apply RouterOS 6.22rc4 to CCR1009, and symptoms of the interface disappears,
it was possible to confirm the automatically restart takes problems when left for a while.
By switching back the same way partition ROS6.21, it was possible to avoid the problem somehow.
Just to be sure.
I have installed 6.21rc22 (build date: Oct/24/2014 10:29:23) on RB751G. It is a critical gateway router. Do you mind letting me know if I am save to upgrade to 6.22?
Thanks.
Upgrading ROS is not save at all. If you are happy with the installed release …
v6.21 had problems on upgrade from RouterOS v5.x, it will go into reboot loop - netinstall solves the problem
if you upgrade from other v6.x all is OK (at least in my network)
I do not know why version was taken down, simple note about upgrade from v5 would be sufficient.
There are too many changes from v5 to v6 for simple upgrade, anyway.
P.S. Where are those people coming from that suddenly (after 2 years) decided to upgrade from v5 directly to v6.21 ? 
Some wait until there is a 6.x Version that does not kill their router. They should have waited longer.
Could be those people who had a stable wireless network and decided to go with capsman. Anyhow thanks for the feedback…
Some of the devices we get come with v5.xx pre-installed. Upgrading is always the first thing we do on those.
It is huge move, that, in my opinion, requires that you start with clean Netinstall, bios upgrade and new config, anyway.
So this issue shouldn’t have no effect what so ever.
That explains a lot. Thanks!
I have old 433ah with preinstaled 4.17. After upgrade to 6.21 is device in reboot loop 
honzam, I’m sorry that you didn’t see this topic or the notice in the download page. Netinstall will fix the issue. We will also re-release the version soon.
I know how fix it. Previos post is only report.
Before release new version → more testing 