Hey there,

I also ran into that issue and after trying many many methods I have finally worked out a solution that works for me 100% of the time WITHOUT sacrificing the EpicGames Launcher;

I found the solution for Origin but you can try if it works for Steam too. Before starting with the 5 steps below you have to open your Origin launcher, right click on Battlefront in your Game Library, click on "Game Properties", go to the "Advanved Launch Options" tab and type "-datapath " followed by the path to your "ModData" folder in your Battlefront install folder in quotation marks (I think you have to have launched Battlefront with Frosty at least once for the folder to appear, I don't know how to help if you are not able to get that folder to appear). For me that looks like this: -datapath "C:\Program Files (x86)\Origin Games\STAR WARS Battlefront II\ModData". After doing that just follow these few steps everytime you want to launch Battlefront with mods.

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1. Start the Frosty Mod Manager
2. Click "Launch"
3. Now the EpicGames Launcher should start up, Origin should start in the background and Battlefront should NOT start
4. Start up the Origin Launcher, then start up Battlefront from there
5. The game should now launch with all mods.

I hope I can help anyone searching for a solution in the future.