I am seeing this issue as well as the people that use my AUR repo when trying to start up Plex. There is also a thread in the Synology NAS forum with the error as well. Not sure how they are related.
https://forums.plex.tv/discussion/220581/plex-fails-to-start-on-ds1815/p7
Attaching full Plex Media Server.log file, but the last line is:
Jun 15, 2016 17:17:34 [0x7f6389bd0800] ERROR - Error: Unable to set up server: basic_string::_S_create
Which apparently means it tried to create a string bigger than std::string::max_size(), maybe from the HTTP GET?