Note that I have since confirmed this issue is also occurring with the normal org package as well as the org-plus-contrib package including the org package in the GNU repository and with org built from sources. Have also reproduced the same error with emacs 25.2-rc2.
Note that the issue only occurs on the first load of an org file with source blocks. If you then kill the buffer and open the same org file for a second time, it loads fine, no errors and the source blocks are fontified. Opening other org files with source blocks also works fine once the first one has been loaded.
This is not an issue caused by mixed org versions. I have done C-u M-x org-reload and then re-installed the org package as well as manually deleted org from the emacs install to ensure only 9.0.5 is available with no change.
At least 1 other person has been able to reproduce this issue.