Do you have any field chunks that are over 2000 characters long, possibly? it says it has a 2000 char limit per field, not sure if that's it.
Also what hotfix version are you on, may be related but may be not, 9.0.11 had a fix for pages:
When the 'Combine with default culture' setting was enabled, accessing a page in an untranslated culture resulted in an error, instead of displaying the default culture version of the page. The error only occurred after applying hotfix 9.0.10.