What I did before
I imaged the raspberry Pi with an minimal debian 10 32 bit, then I used this cool installer I have found in the world wide web.
https://community.ui.com/questions/UniFi-Installation-Scripts-or-UniFi-Easy-Update-Script-or-UniFi-Lets-Encrypt-or-UniFi-Easy-Encrypt-/ccbc7530-dd61-40a7-82ec-22b17f027776
6.1.71 died with
1
2
2021-04-28 18:02:11,486 main ERROR Error processing element InMemoryAppender ([Appenders: null]): CLASS_NOT_FOUND
2021-04-28 18:02:12,662 main ERROR Unable to locate appender "InMemoryAppender" for logger config "root"
What I did then?
I just upgraded using the same script mentioned above to a release canidate Version 6.2.17.