Thanks for mentioning that @vvanpo 
I managed to get this working but do not know where to link <subfolder>/user_avatar/<domain>.
There is no user_avatar folder in the public folder. Where have you pointed (dest) your user_avatar symbolic link placed into <subfolder> ?
Thanks 
Edit: It seems to work without user_avatar link. Maybe images must be rebuilded in background (sidekiq tasks) and this just take some time.