If a sapling from Forbidden Arcanus undergoes growth, the server will crash.

You can use the Item Banning mod to temporarily ban them until the pack updates to the newest version of Forbidden Arcanus.
https://www.curseforge.com/minecraft/mc-mods/item-banning

/itemblacklist ban forbidden_arcanus:cherrywood_sapling
/itemblacklist ban forbidden_arcanus:mysterywood_sapling

Could you include a log file of the crash for both the server and client?

https://www.toptal.com/developers/hastebin/oducapezex.properties

I already tested this, you can see for yourself if you place some saplings in your world and wait a while in daylight. It will eventually crash. The devs in the Create Technical Discord are already aware.

Duplicate of #237