Did charging to 100% behavior change recently?

Recently, it seems like when I charge my FR255 to 100%, it doesn't run very long before dropping to 99% and then the discharge rate goes back to normal for ticks after that.

In the past, it was the opposite, where it would linger at 100% for a long time, as if it had some extra, non-reported capacity "above" 100%.

So, I'm wondering if the charging logic now stops earlier or if this is an early sign of battery degradation. I'm using the same USB charger and unattended charge durations as always.

I don't always operate in regular smartwatch mode after a charge, so I'm not sure if this changed recently and correlates with a firmware update. (Often, I charge and then go do a GPS activity, so I'm not aware of the 100 to 99 transition timing...)