Hello!  We have received some reports of connection issues to servers with the latest 1.90 update. We are currently investigating the issue, and would like to open a discussion regarding the update. If you have any questions or concerns regarding the update feel free to reply to this thread.    Tips:  If you are experiencing a connection issue whereby you're getting "session lost" upon connecting to a server: 
Please try switching to the Profiling branch (code: CautionSpecialProfilingAndTestingBranchArma3) on both the client (primarily) and the server.  As of now the branch contains improvements and more informative messages/RPT logging about the cause of the disconnect. More details about the Profiling branch can be found in the dedicated thread.   We've discovered the issue might be connected to some addon files that shouldn't be there. air_f_rtd.pbo, dubbing_radio_f_data.pbo, missions_f_epb_data.pbo, missions_f_epb_video.pbo, missions_f_epc_data.pbo, missions_f_epc_video.pbo, sounds_f_weapons.pbo should be removed from the addons folder. These addons are deprecated and should no longer be present in the addon folder (Steam doesn't autoclean them). If deleting these two files doesn't help, please delete any other pbo that pops up in the connection message, or alternatively delete the entire addons folder (including those under DLC folders), and verify the integrity of your game files to have the proper addons re-downloaded.
If that doesn't help then:
And, please, let us know if it helped (eventually what exactly helped)! Thank you!