A beta of AltStore has been released to fix an app crashing issue caused by server side change on January 28th.
The AltStore team identified the problem on January 29th:
Due to some server-side changes, AltStore and other sideloaded apps installed after January 28 will now crash on launch. We’ve identified a fix and plan to release an update soon, but for now we recommend NOT refreshing any apps to prevent them from breaking.
A new *public* AltStore beta is now available! There are still some bugs we need to fix before an official release, but for most people this should fix apps crashing