Cannot change the site logo thumbnail

Victoria Symons 

Hi, I have been fiddling around with this issue for some time now and I don't seem to have a fix that permanently works.
What I do have is some fixes you can try, but might not always work, or only work partly. They are combined into this instruction

1. Get the picture you want to use for a thumbnail, and name it "__siteIcon__" (double underscores in front and at the end). Just that name and nothing behind or in front of it. 
2. Make the picture a JPG format, this seems to be working the best for me. Also try to make it small in size, I have mine at 256x256.
3. On your SharePoint Homepage go to Settings > Site Contents > Site Assets. There you can delete all the old images you used for the thumbnail (I believe all files with __siteIcon__ in front of it).
4. Drag and drop/upload the local JPG file you just created to this library. Quickly after select the file, and check it out (for me the three dots in upper right corner)
5. After this refresh the browsers cashe (Crtl + F5). It might take some time for the thumbnail to update across all sites. 

I hope this helps you!

Lucas