Based on a forum post from back in 2014, the Sigil of Compression from the Blood Magic mod was banned for causing server lag or crashes. However, since then this bug has been fixed by the mod's creator, as they have posted on their GitHub in February of 2015. As of Agrarian Skies 2 version 1.1.13, the pack uses the 1.7.10-1.3.3-11 version of the Blood Magic mod, which was pushed as the release build in July of 2015 - after the aforementioned fix for the Sigil of Compression bug was implemented. Since the Agrarian Skies 2 server is now on version 1.1.14, is it possible to remove the ban on the Sigil of Compression? It's quite a useful item and it seems a shame to keep it banned if the underlying issues have been fixed.
I don't think it is the same bug but I unbanned it for now so we will see if it causes issues again. (Needs server restart)
Thanks! I'll be sure to report any obvious problems I notice when using it. EDIT: Just did some (very heavy-duty) testing, and it seems like the server handles it just fine - not even a small lag spike when converting inventories full of blocks, even while still picking up new blocks at the same time. Maybe you can see some issues from your server-side perspective, but from here it seems like the Sigil of Corruption is satisfactorily fixed.