when checking the arch sources for the sddm package, the apply a fix that will be released with sddm 0.14.1 : https://github.com/sddm/sddm/commit/ecb903e4.patch. Maybe this will help resolve the avatar issue.
https://github.com/sddm/sddm/pull/684
Neon will get it when SDDM makes an upstream release.