There are two other possibilities. One, as MrGimper says, and the other that your cabinet had a power cut and you were one of the early resync's.
I would tend to leave it alone and enjoy. It may do similar again soon and lower it to 4dB, or noise/errors will rebuild and cause it to revert to how it was before. A single re-sync in daylight hours might answer the question, but would either disappoint if it was a power cut causation, make little difference if it was G.INP kicking in, or slightly delay a further drop to 4dB with higher sync still if it is DLM seeing how low it can take it with acceptable error rates.
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