This breaks some of the heavily modded servers (like ATM9), since this essentially can be placed by any player on the server and be offloaded into abyss, requiring external tools to find the block or to prevent people from placing it alltogether.

What do you mean by "offloaded ticking"? The shifting sundial and cloudshifter should only update like regular block entities, whenever they're loaded.

Thats strange, for some reason in ATM9 pack if you place sundial or cloudshifter and TP 15k blocks away - they would still function as if they were still loaded. Could it be some other mod doing this then? Because this is only happening to these two blocks on our server, so my initial assumption was that they are handled separately by the mod somehow.

That's odd! Would you mind trying to reproduce this issue in a world with just Nature's Aura (and Patchouli) installed? I'll also do some investigations about this once I have an opportunity :)