0.First and foremost, be sure you have your mods located inside the "mods" folder along side the rest of the main files such as Storage and assets folder.
(ex: [...]\Starbound\mods)

Here are 4 simple stages when encountering missmaching assets on joining the Starbound PLUS server :

1.Check if you dont have some extra mods or a missing one.
If you are using steam, be sure to UNSUBCRIBE to ALL mods. (you can also manually check here : [...]\Steam\steamapps\workshop\content\211820)

2.Maybe you have an unwanted file located in the asset folder for ex: _metadata, or anything other then the game's assets an songs.
The assets files are located here : [...]\Starbound\assets

3.If you are not afraid of reading log.files you should examine it to find the intruder more easly otherwise skip to Stage 4.
The log files are located here : [...]\Starbound\assets

4.Contact the PLUS TEAM or declare your issue on ours discord in "support" channel.
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the website host is sick so the modpack may be out of date currently at the time of this posting we are on 4.2.2 a patch can be found here just copy/paste or move the mods from the patch into the mod folder and pick the replace option when you get the pop up.



if you still have issues check the starbound plus discord channel stickies (the pin in the top corner) to see if there was a new update.