Hi, I thought it was more appropriate to move this thread to "Help & Technical Support" since this is a common question and is more about how the game manages mods than modding itself.

If the game makes you redownload the same mods when you join another player's lobby, it most likely means your mod versions aren't the same. Otherwise, if you share the same version, you shouldn't be redownloading them.

To avoid redownloading mods, you must make sure your mods are up to date in the mod settings menu and if they are and the game still makes you redownload them, it's possible that it's the host's mods that need updating. Some people host dedicated servers that stay up for a long time and if they are using mods that had a recent update, they have to shut their servers down in order to download the updates.

@The Flaming Pike thank you