UPDATE: Ownership will be transferred to @paul and the instance will remain active, announcement post
Ninja, the owner of the instance, is retiring from naturist advocacy for personal reasons, and is therefore closing the instance. He mentions he's open to transferring admin to somebody else as long as his data privacy concerns about the transfer are addressed, otherwise the instance closes in July.
pl.nudie.social is only one of two Mastodon instances oriented towards the naturist community, the other being body.social, which is notorious for not requiring Content Warnings for nudity, which naturally puts it at odds with other Fediverse instances.