Some of you may have noticed that, from Thursday, Nov 9, 17:30 UTC to Monday, Nov 13, 20:45 UTC, we were providing the short chain by default for certificates issued from R3. This was an accidental misconfiguration, and has been reverted.
However, the change observed over the past few days is identical to the change that we will be making on February 8, as announced above. If this change caused issues for your client, please prepare now for the upcoming changes. The blog post linked above has details on how.