I am very curious about how Obsidian could be able to wipe out Time Machine backup data. This would seem impossible to me, since backup data lies safely on a separate disk (usually, that is).
I am also puzzled by the fact that this only affects backups since April 12th, and only backups of the vault and no other files.
Time Machine has its very own file structure, and in order to delete only a specific set of files (your vault) from the backup, and only back to a specific time (Apr 12), would require quite specific search and delete operations via Time Machine AFAICT.
What might have happened (but I am only doing wild guesswork here):
When TM cannot reach the backup disk, it creates local snapshots until the backup disk becomes available again.
UNLESS, however, you have disabled local snapshots for some reason.
Now let’s assume that TM was unable to reach the backup disk since April 12th, and it also created no local snapshots.
And then, something happens and the files in your vault get erased. As a result, the actual files are gone, and the TM backup has no backups since April 12th.
So I would treat the vanishing of local files separately from the non-existence of backups since Apr 12th. Maybe there are really two different reasons for that.