I run a survival server with a minimum of 5 gigs and max of 10g with only 1-7 people playing. There is a little amount of lag and some skipping ticks but whenever I go into a nether portal from the nether the server times out. Throw an item into that nether portal it times out again, anything I do to load the chunks on the other end of that portal will time out the server. The chunks on the other end of the nether portal are glitching out and this only started happening in versions of 1.12 and above.