While roaming through old Codeforces contests, I found a strange gap from early 2014.
A whole series of consecutive Div1 and Div2 rounds has zero difficulty ratings on their problems:

• Codeforces Round 229 (Div. 2)
• Codeforces Round 230 (Div. 1)
• Codeforces Round 230 (Div. 2)
• Codeforces Round 231 (Div. 2)
• Codeforces Round 232 (Div. 1)
• Codeforces Round 232 (Div. 2)
• Codeforces Round 233 (Div. 1)
• Codeforces Round 233 (Div. 2)

Does anyone who was around back then know why this specific stretch was skipped? Did these rounds run into contest-day issues, or did the rating calculation script just bypass them?