Icingaweb2 was updated to 2.12-1 and later apache was updated to 2.4.6 . Now Icingaweb2 UI won’t work.
Forbidden You don’t have permission to access /icingaweb2
I understand the issue is specific to apache 2.4.6. I came across this and tried out but it didn’t work.
https://github.com/Icinga/icinga-web/commit/27c1eed53e68be5400bf1dd68de95bc6073b06b7