Sponge Server Messes Up Singleplayer Worlds

Hello everyone.

I play Minecraft singleplayer and sometimes I play it with my friend, through a private Cauldron server I’ve set up for 1.7.10. When I do so I just move my singleplayer world to my server, then move it back when done.

Recently I decided to upgrade to 1.8.9, since there’s no Cauldron anymore I set up a new sponge server for 1.8.9, made sure all mods are updated and installed, and popped my singleplayer world into the server.

When the server begins to launch the console complained about a bunch of missing blocks and items (including modded ones and vanilla ones, even though I’m pretty sure all the mods are present) and tells me whether to type “/fml confirm” to proceed or “/fml cancel” to cancel.

So I typed “/fml confirm” to proceed, went into the world and wow. Some of the blocks are messed up, for example all jungle fences are turned into bedside drawers (from MrCrayfish’s furniture mod), all darkoak fences are turned into jungle fence gates, all slime blocks are replaced by oven overheads (again from MrCrayfish’s furniture mod)…

If I don’t use sponge, my world loads normally on the server but I will experience terrible server lag because of my not-so-great computer. What should I do to overcome this problem? Thanks in advance.

I’m using spongeforge-1.8.9-1890-4.2.0-BETA-1693.

By the way, I think it’s worth mentioning that when I launch the sponge server, the console gets spammed with a lot of error messages like “method overwrite conflict for…” "

Not sure if this has something to do with the missing blocks and items.

Doesn’t have anything to do with that, that’s only to do with entity collisions, and everyone sees that.

Oh okay, so now what about the sponge server messing up the blocks issue?