The preservation block causes the client to crash if placed from the inventory, while HWYLA is installed:
https://pastebin.com/qecEMq2k

Seems like HWYLA catches it at some weird point in time, it works fine after the client is restarted. Or right after encasing a mob in amber.

I tried to report this to HWYLA first, since IMO it shouldn't drag the whole client with it if it fails to getPickBlock, but they insist it's a bug on Erebus' side.