I just updated to version 9.0 (elpa version Nov 18) and experienced issues with the custom agenda views in column format.
I had previously specified my custom agenda views using: org-agenda-overriding-columns-format %Custom1 .... etc. 
After the switch to version 9, I only got the default column format output: %25ITEM %TODO %3PRIORITY %TIMESTAMP, when I selected my custom column agenda view––although each column still had the custom column name, the column content was populated according to the default format (%25ITEM %TODO etc.).
I found a workaround by substituting org-agenda-overriding-columns-format %Custom1... with org-columns-default-format %Custom1 .. for each custom view.

I could not find a reason why version 9 would not allow me overriding the default column format–any suggestions?