For the past month and what looks to be during the EGPRN Lille meeting the French Railway workers will be on strike. There will still be plenty of trains from Paris and Brussels arriving and leaving Lille but some trains may be canceled. Although as of now (April 26th) the cancelations in May is not so clear delegates coming to Lille by train should check the SNCF webpage for updates and cancelations.
Besides train, Lille is easily reachable by bus services from various European cities and airports nearby. Please consider such alternatives. Below are some bus providers:86th EGPRN Meeting, Lille-France, 9-12 May 2018 Announcements on 4/26/18, 9:00 AM.