I hit the same issue and was searching for some history on it. Unfortunately, I lost all the links I read to form the conclusion except for the final link...

Check this out. Seems to be the cause of this issue and it is fixed in a later version. You should be good if you have upgraded:

https://support.microsoft.com/en-us/help/3011465/fix-sequence-object-generates-duplicate-sequence-values-when-sql-server-2012-or-sql-server-2014-is-under-memory-pressure