[Kerbal Space Program] I installed mods on a previous version and since the game updated, it's now acting weird or flat out crashing. Why is this?

Mods are very likely to break from one update to another, and so we suggest you delete your mods and wait for the mod maker to officially state that they work with the newer version before downloading and installing them again. Another option is to roll-back the update to the previous version where you know mods work fine. Instructions to do that on Steam can be found here. For the Private Division Store, since updating is on-demand, if using mods it’s recommended to hold from updating to a new major version until you know all the mods have been updated. If you already updated and want to roll back, downloading the previous version installer and using it over the same folder should do the trick.