Looks like it’s not able to find the button images
Open up the button settings and expand >Tabs and check the up and down image paths point to where the images should be.
Eg. Button Page 1
UP /Users/User/Documents/Silo/2.5/Preferences/Presets/Button Settings/Custom Images/modify_tab_up.png/
DOWN /Users/User/Documents/Silo/2.5/Preferences/Presets/Button Settings/Custom Images/modify_tab_down.png
Did you have Silo previously installed and displaying the correct buttons or is 2.5.2 the first install?
That solved the problem! Very odd.