Anyway, I am mumbling about upgrading to the Mi6, just because... you know.. this thread!
I can't advise on that, I usually buy stuff when I need it or the old breaks, not because it's new (or new version)

Are you using an iPhone or an Android paired with this band? It never happened to me with both Mi Band4 and 5.
Try deselecting the notifications and turn those back on, probably the phone is sending twice to the band because two channels are activated.
I have Android phone, an older Redmi, so the compatibility should be great (I hoped). Just it's Android 8.1
I've stopped the notifications for Telegram and one came onto phone and not band - good.
I've started the notifications again on the band and .. they're get doubled again.
Oh well, if anybody finds out why, please write and add my name so I get notified (twice!).