FWIW - I only had a problem when I imported from Classic. My Classic avatars were all 64x64 but when I set up Threads, I changed my default to 72x72. Importing all the 64x64 avatars resized them to 72x72 in Threads. What I had to do was run a query that Rick gave me to resize all the avatars to 64x64 (they're actual size, despite the max) and all is well -- even newly added/uploaded/user avatars are displayed properly if they're smaller than 72x72 (my max), and if they're larger, they're resized to 72x72.
