Looks suspicious, but there were 4 vessels in the area whose transponder signal was lost by public trackers during that night.
It has also been pointed out that this is a location with lively traffic. So if it turns out that is was an anchor (as in the New New Polar Bear case) that's extra suspicious because anchoring in such location is not normal. On the other hand if it were explosives like in the Nord Stream case, they could have been applied also weeks before.