I'm pretty sure this world contains data from an old version and upgraded 0 chunks are mutually exclusive ideas. When there are no chunks in the cache, and there is nothing to upgrade, Bobby should not post anything in the chat, and it should not offer to upgrade anything.

The following message should never happen. When there is nothing to upgrade, Bobby should say nothing, rather than recommending that you upgrade the nothing.

Same problem here.

I have the same problem ("upgraded 0 of estimated 0 chunks").

It happens for me in singleplayer when Dynamic World management is enabled. Setting Singleplayer Server View Distance to zero disables Bobby in singleplayer and therefore "fixes" the chat message, but obvious disables bobby, which is not desired.

This can happen when the world metadata needs to be updated.

It should however not happen repeatedly.
If you have a world where it happens repeatedly, please attach your bobby config file and a zip of your .minecraft/.bobby/<worldOrServer> folder where this happens, as well as information on which specific Minecraft and Bobby version you're using.

Edit: Oh, also just noticed that it'll always happen once when first joining a world/server with the new Dynamic World management is enabled. That'll be fixed in the next version (5.2.0).

Assuming everyone with this issue had "Dynamic World Management" enabled, this should be fixed in the just-released version 5.2.0.

If you did not have "Dynamic World Management" enabled, please open a new issue and include aforementioned details required for reproducing there.

Can also confirm this happens.