This is likely an old spirit tree planted before the update, it wasn't expected that they would die, although any future trees you plant should grow properly.
Thank you for the reply. I planted another one after the update and it became diseased as well...I will try another one and see if this still happens!
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Only issue I've noticed is Spirit trees say "Prune" instead of "Check Health" and you don't get xp from them. 
