Bug Report: Variations that replace vanilla difficulties will be ignored after exiting to Freeplay

[dombomb64]

Issue Checklist

• [x] I have read the Contributing Guide
• [x] I have checked the Issues/Discussions pages to see if my issue has already been reported
• [x] I have properly titled my issue

Platform

Compiled from GitHub Source Code

Browser

None

Version

0.6.4

Description (include any images, videos, errors, or crash logs)

If a mod adds a variation that replaces an existing difficulty, the variation will be replaced with the vanilla counterpart after the player exits said song, regardless of the difficulty or variation they chose to play.

Here is a video of me showing how this bug is triggered using a custom nightmare mix.

Note: Despite the use of mods, there are no active scripts that could be messing with how Freeplay loads the songs.

https://github.com/user-attachments/assets/cf4b17ab-6e24-4d59-accf-bfa43f910886

Steps to Reproduce

Here is an example mod to test out the bug. The song replaces Senpai's nightmare difficulty. difficulty-replacement-bug.zip

1. Install or create a mod that replaces a vanilla difficulty via the intended _merge folder method.
2. Go to Freeplay and enter the song.
3. Exit back to Freeplay.
4. The replaced difficulty remix is now reverted to vanilla until you refresh or restart.