1. Trade farmers carrots for emeralds.
2. Carrots are being added to the inventory by a nearby water stream, and added to the open inventory slot at the bottom right
3. In the first trade, receive a few emeralds, which are added to the top-left inventory slot
4. With each trade, there's a chance that a stack of emeralds disappears. Usually it's a full stack that disappears.

Without this mod, emeralds received in trade are placed in the first open inventory slot at the bottom right. Not sure if that's related this issue.

What kind of server is that? (Builtin Single-Player, Vanilla, Fabric, Forge, Spigot/Paper) ? If it's a Spigot/Paper version, is the server version different from 1.17.1, with a plugin like ViaVersion to translate between versions?

Are you using the newest (1.17.1) version of the mod, or a previous one?

The mod simulates filling the trade inventory, then shift-clicking the trade output item. This typically means the shift-click occurs before the server responds to the "fill the inventory" clicks, which might mean the client assigns a different slot than the server does later. But this shouldn't make content disappear completely.

This was running in single-player on 1.17.1 with the easiervillagertrading-1.17.1-fabric0.36.1-1.5.4 build.

I am experiencing the same issue but with Sticks and Rotten Flesh instead of Carrots. Using version 1.18-fabric0.43.1-1.5.4 from modrinth on a Vanilla 1.18.1 multiplayer server.

This is happening to me as well when I trade too quickly. The server is running Paper (latest 1.18.1). Specifically this happens when i spam click the item instead of shift click.

I'm experiencing this when using shift+click (trade all) with sticks to a fletcher, Fabric 1.19.1

A few things I want to add that I found out:

Emeralds (or traded items) seem to disappear when the trade is repeated too fast
For me this does not happen when using Shift+Click to trade all
This can be replicated easily by using an autoclicker

Also my suggestion (if this is an unfixable MC issue) would be to add a hidden timer that limits single trades to once every x ticks

Technical information in my case:
Pufferfish/Purpur 1.19.2 server
Fabric 1.19.2 Client
Latest Mod version