toeto Thank you for submitting your Spine project!

Regarding the first problem, since you have disabled Auto Key, when you hide the attachment in this state, the color of the key next to the slot will only change to orange and the key will not change until you press the Key button. Also, when you restore visibility, the color of the key returns to its original color. This is the expected behavior.
However, it is confusing that once the key color changes to orange, the orange color remains while the timeline bar is scrubbed. I think this is something that should be fixed, so I will create an issue ticket for this later.
(If this is not the problem you are having, please let me know.)

Regarding the second problem, while checking your Spine project while organizing it a bit, the following error was displayed:

Was this Spine project originally created with an older version and reopened with 4.2? In rare cases, there may be a problem with data created in an older version of Spine that is corrected when opened in a newer version of Spine. In this case, rather than a bug in 4.2.36, there may have been a potential problem with the original data. I haven't reviewed it thoroughly yet, but if this Spine project is an upgrade from an older version, and if you still have the older version of the Spine project, it would be helpful if you could send it to us as well.

I have created an issue ticket for the first problem: EsotericSoftware/spine-editor822
As for the second problem, I am still looking into the details, so please wait a while.

@toeto Perhaps I found the cause of the second problem. The problem seems to be that in one project the eggshell_fill slot is under the hip bone, while in the other project the eggshell_fill slot is under the eggshell_defense bone. The animation that has the problem has a key for the eggshell_fill slot, and as a result of trying to import that timeline, the timeline that should be imported into the hip bone is imported into the eggshell_defense bone. However, I am not sure if this is a bug or not, so I will confirm this with the Spine team.

toeto Thanks for sending us your old Spine projects! I tried to reproduce the same problem in 4.1, and in the process I found that when such a problem occurs with an animation with separate translate X/Y, only the state of the separation is imported into the bone of the same name. But the actual translate X/Y timeline is imported into the bone that has the slot, causing the error. In other words, there seems to be no problem with the upgrade from 4.1 to 4.2 itself.
I am still confirming the correct behavior of importing when the same name slots are on different bones, so please wait a while.

@toeto Regarding the second issue, we have confirmed that it is probably a bug, so we have created an issue ticket here for a fix: EsotericSoftware/spine-editor826
We apologize for the inconvenience, but please wait until we have resolved this issue.

toeto Unfortunately, this issue has not yet been resolved. We will be sure to update the issue ticket as the fix progresses, so please check it for updates.