It seems, that OS 2.3.4 is blacklisted because there's a bug AS-45527 which causes missing current volumes from the UI and it would be fixed in 2.3.6.
Thanks for posting this Roland.
We have proactively spotted a bug in 188.8.131.52 which affects roughly 1% of systems within the field when upgrading to the 2.3 code. For that reason we have blacklisted the firmware from all systems and will be releasing 184.108.40.206 with the appropriate bugfix shortly.
This does not affect any customers that have already successfully upgraded to 220.127.116.11.
All customers who have downloaded 18.104.22.168 but not upgraded have been proactively notified of this issue. At this time it's advised not to upgrade.
There's not really much more to add than that, so i'm going to lock the thread. If anyone has any questions they can reach out to Support.
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