Thanks for all the hard work going into the server update Spec!  Here's the error code I get when trying to log in, if it helps.

Internal Exemption: io.netty.handler.codec.EncoderException: java.lang.Null PointerException: Cannot invoke "com.github.retrooper.packetevents.protocol.item.enchantment.type.EnchantingType.getId(com.github.retrooper.packetevents.protocol.[;ayer.ClientVersion) because "enchantment" is null.

This error has changed to Internal Exception: java.net.SocketException:Connection Reset

All fixed. Disabled the plugin causing the problem and pending an update for it!