On pre 1.13 servers, all enchantments are managed by their unique IDs.  If you have custom enchantments installed on your system using plugins like TokenEnchant, your system might have enchantment with randomly assigned ID numbers.  Minecraft servers do not have a mechanism to ensure the consistency of those randomly assigned ID numbers.  

As of v18, TokenEnchant has its own Enchantment ID management system for pre 1.13 servers.  Before you upgrade your TokenEnchant to v18, it is strongly recommended to install this tiny plugin to generate "enchantIDs.yml" file which lists all registered enchantments and their IDs.

Once you generate "enchantIDs.yml" with your pre TE v18, you can install TE v18 and copy the generated "enchantIDs.yml" into TokenEnchant's plugin folder.  Then TE will maintain your old IDs under TE v18.