Hi,
I have experienced a bug like in the following screenshot: https://drive.google.com/file/d/1ureKCyQAXlsfl9mjMO7vWQItYwfFEOhd/view?usp=sharing
I have added new items and battery is charged, but train thinks that I have no controller. There is no place for fuel too.

additional issue - I couldn't pipette items in the train equipment grid

I really like the idea - could it be possible for you, to do the same for https://mods.factorio.com/mod/cargo-ships?

I have had this problem too, until the dev releases a fix, you can get the train to convert into the correct entity by driving it, either in person or remotely, and then immediately exiting. Any blueprints of the train after doing this will work without having to do this, however.

I have had this problem too, until the dev releases a fix, you can get the train to convert into the correct entity by driving it, either in person or remotely, and then immediately exiting the train. Any blueprints of the train after doing this will work without having to do this, however.

What did you do to make that train and the equipment? I want to repeat the same steps so that I can debug it. Please try it with only the controller and engine, as that would be easier to test.

When I tested the trains, I inserted equipment with the drop item command (Z), and that worked for me.

Open the fuel gui, click the item in my inventory, click the item into the equipment grid, the train will remain "unpowered" until it is driven manually. I only have controller and engine at this point in my playthrough.

It is not possible to open the fuel gui when there is no locomotive. I placed a locomotive from the character's inventory and then followed the steps you described for a controller and an engine, and it did not reproduce the bug. The locomotive became "Condenser engine" when the second equipment item was inserted.

Unfortunately, I can't identify the problem with the information that I have. If you find a sequence of steps that can reproduce the bug, please describe it and I will try again.

I am aware of some bugs when construction bots are involved.

Sorry, the train is already placed, by hand or by bots, doesn't matter. However, it appears that something has now changed and when the engine and then also the controller are inserted it converts correctly, however it kicks me out to remote view. Also it now appears that I can insert items directly from the engines, but now can only remove them using bots, I can't drag them back into my inventory.

It does matter. Code in a mod that detects when entities are placed by a player will not detect when entities are created by construction bots. Two different pieces of code are needed, and trying to debug one of those when the other is broken would be a waste of time.

It is a known issue that the train GUI closes when the train is reconfigured.

The inability to remove locomotive equipment from the remote view is built into the game engine. The same behavior occurs in other mods where locomotives have equipment grids. You can work around it by riding the locomotive and opening the vehicle's equipment grid using the button in the corner of the screen, near the character's ammo.