Unfortunately, ArsMagica had to be removed:
- It turned out to be buggy, and there was a reported known bug with it crashing servers.
- It bypassed chunk claims and fixing that problem isn't, in our opinion, worth the trouble.
- Not a lot of gameplay time for a mod that's relatively big (10 MB).
An update 13a was pushed which removes ArsMagica, and it is technically an optional update. Removing ArsMagica saves you a bit of memory, however. The mining world reset scheduled for May 4th is still going forward.