It sounds like a weirdly specific thing for a bot to do.
It could be a case of the Baader–Meinhof phenomenon:
Frequency illusion, also known as the Baader–Meinhof phenomenon or frequency bias, is a cognitive bias referring to the tendency to notice something more often after noticing it for the first time, leading to the belief that it has an increased frequency of occurrence.The illusion is a result of increased awareness of a phrase, idea, or object – for example, hearing a song more often or seeing red cars everywhere.
Oh that's bad. Good luck getting rid of them.
I personally find downvotes useful because there are a lot of low quality comments and content. Downvotes help me (and others) to avoid seeing them. Thus not wasting time with uninteresting posts or comments. But you aren't supposed to downvote everything that someone says.