After reviewing your posts and comments in the community, it seems you experienced issues when upgrading a cluster. While I would be very happy to look into the support details for your case, please note, this specific discussion is about management.
Also, a single case of an unsuccessful GW upgrade does not qualify as "the version is very unstable", even if your own experience with it was not ideal.
We closely monitor statistics for each release, and I have enough data to insist on what I said, both releases are stable, especially when it comes to the management server, which is the focus point in this discussion.
I will be happy to reach out and discuss the issues you may experience with R81.20, if you need, though.
We value your feedback, and we always working on improving the products.