Bug/Issue Family not able to connect via IP to me

Hi! I have following problem: My family and I have been playing Stardew Valley, while I've been hosting, with no problems whatsoever.
Today I re-installed Windows and now they're not able to connect to my game anymore. We always play over Lan only, since it gives the least amount of lag. I've got no clue, why it doesn't work anymore.
I've tried re-installing the game, nothing. I do have the option of IP connection turned on. My firewall does not pop up at all for the game either.
I hope someone can help us :/ We don't want to start over since we just reached Winter