I am running a multiplayer PVP Sea Block (freeplay) server with FNEI (0.1.8), default mods from the Sea Block Pack, and while it can be used when no one else is on the server, it appears to be causing a desync of players when there are multiple players on. I was able to find the desync log and added it to a pastbin here.
https://pastebin.com/WbR1i6kg
If there is another place I need to look for an error when this desync occurs please let me know and I'll get you all the information I can.
Didn't know if this was known issue, as I've seen it mentioned here in different places and the changelog states that the issue was corrected for a particular instances.
It seems be tied to the search function, when clicking an ingredient to find out how to make it within a recipe. May also be a bit of a memory leak as a restart does correct it for a time, but only for a few hours depending on server activity.
Hope this helps, this is a great tool, especially when using mods you are unfamiliar with.
Thank you for your hard work and time.