In some cases an update may cause a mod loader or specific mod to stop working correctly, and any save file which is dependent upon those mods will not successfully load.
One option is to try to reinstall the mod loader, and then try the mods themselves. In some cases you may need to wait for the creator of the mod to make an update to make it compatible with the latest version of Slime Rancher.
Unfortunately, once a save file has been changed by a mod it is out of our hands; there isn't any way for us to undo it.
One thing you may want to do is to make a backup of your save data before installing any mods.
In some cases, it may not let you successfully create a new game as well, which may require a complete reinstall of Slime Rancher to solve the issue.
If you have any trouble with getting Slime Rancher to work after removing mods, please submit a ticket to us and we will do our best to help.