A few times around 2017, yes.

Has it happened during a bear market? I can't recall

Nothing as severe as this, no.

Interesting times we're living in

👍🏼

But only by accident or some strange one-off??

There are some reports that B cashers were 'spamming' the chain but generally speaking it was the overall market mania that drove it. Also back then far less exchanges used batching.