Redmine

Yes I am also not sure why that is. I have the same problem too.

Can that tool clone and snyc redmine instances?

it can only transfer tasks between Redmine instances. if you need full cloning (projects, users, tasks, comments, files, attachments,...) you have only 1 choice: establish database-level sync. full cloning via some remote APIs, especially as immature as in Redmine, is unrealistic.

Can this issue sync get automated and run on linux? What happens if categories, versions or projects are missing for issues getting synced?

Task Adapter is currently a desktop application, which runs interactively. the new 2.0 version ( https://www.hostedredmine.com/projects/ta/versions/845 ) will have a web-UI and is planned to support running scheduled tasks (although scheduled tasks can be moved to version 2.1).

if categories, version or projects are missing, sync will fail in the current TA. whether or not to support auto-creation of the required fields is not decided yet (and can be impossible for Redmine because its remote API is very limited, plus Redmine development in general has pretty much stopped).
I've been asking Redmine devs to release the new version with some new API for a long time - no reaction.
I think they lost interest in the project.

I've been asking Redmine devs to release the new version with some new API for a long time - no reaction.
I think they lost interest in the project.

Ich hope no, else they should recrute new developers

I monitor Redmine repository, trying to get a feeling of their development path - what's the dev speed, velocity, which direction the project is going, etc.
I see there's a lot of small fixes in version control systems support - I honestly have no idea why somebody would think that's an important thing to work on, but it's their business...
I don't see a clear roadmap or even an attempt to describe which direction Redmine will go in the future.

I'd love Redmine team to review tons of patches people have been sending to them and work on what's most requested by the community. I even offered to spend our team's time to help with the release - no reaction.
The UI requires significant updates to become "task-oriented" instead of "editing forms and tables". (e.g. a link to "close task" or "Start progress" instead of a bunch of mouse clicks: "edit task - select status - scroll 2 pages - click save").

Having a good remote API is crucial too because it enables inter-operability with other systems, which locks people to Redmine even more, so it should benefit Redmine team a lot.
There's a lot of requested features, which would benefit many users, but they are not the features I see patches for in Redmine code repository.

I was very excited about this project about a year+ ago, but my optimism has faded since then.
It's very sad they could not overcome internal problems and had to split into 2 projects: redmine and chiliproject. this confuses people and turn them off from both of the projects. Redmine forums are almost dead.

I think Redmine really had a great opportunity and maybe still has it now, but this is fading fast...

This is sad because I have invested enormous amount of time into supporting Redmine (I created Redmine Java API plus that Task Adapter app, where I had to pretty much guess how API works - that took a loooooot of time).