I would like to share a quick way to generate or rengerate thumbnails manually. I needed this because I migrated from another component so I had a SQL top copy data form old DB tables to CB tables. I was able to copy all 'avatar's but the thumbails were not created due to manual copy.

1) Connect to your server using putty
2) Naviage to public_html/images/comprofiler
3) Run below command to generate full size thumbnails, change *.jpg to suit your need
for f in *.jpg; do cp -v -- "$f" "tn$f"; done
4) Run below command to resize thumbnails
mogrify -resize 85x85 tn*.jpg

I am still testing if this broke anything, but so far looks fine.