It's only a Safe Harbor if you follow the rules
For an online service provider to take refuge in the DMCA Safe Harbor for user uploaded content (17 U.S.C. § 512(c)), it must designate an agent with the US Copyright Office.
In December 2016, the Copyright Office issued a rule to replace the old paper based system for designating an agent with an online DMCA agent registration system. Service providers had until December 31, 2017 to re-register their agents to ensure their DMCA safe harbor protection would not lapse and expose them to copyright infringement claims (see blog post). If a provider designation lapsed and the service provider subsequently re-registered its agent, the provider would still be liable for any infringements that occurred during the lapse because a service provider "cannot retroactively qualify for the safe harbor for infringements occurring before the proper designation of an agent under the statute." BWP Media USA Inc. v. Hollywood Fan Sites LLC, 115 F. Supp. 3d 397, 400-401 (S.D.N.Y. 2015).
As I mentioned in my November 14 blog post, the first wave of DMCA agent renewals for the online registration system has begun. Don't let your agent registration lapse. Otherwise you are increasing the risk that you could be liable for copyright infringement based on user uploaded content.