I jumped in to repair the talk page itself, however someone should investigate what went wrong.
On 7 April 2020, the Flow talk page manager archived the page. I assume(?) this was initiated by the user opting-in to Flow.
- It used the the expected edit summary (Adding archive template).
- It added the expected archive header and category.
- Oddly, it also repeated the Welcome message that was already present.
On 30 April 2020, the Flow talk page manager de-archived the page. I assume(?) this was initiated by the user opting-out of Flow.
- It used the the expected edit summary (Removing archive template).
- Incorrectly, it added a second archive header.
- Oddly, it also added a third copy of the Welcome message.
Possibly relevant clue(?): The Welcome template that was on the talk page is normally supposed to be substed but it wasn't. The Flow talk page manager left the Welcome template intact, and each time it added a subst version.