A bugbear's long-limbed trait says
When you make a melee attack on your turn, your reach for it is 5 feet greater than normal.
Suppose the bugbear has multiple attacks on its attack actions and takes them without intervening movement (or triggered reactions/bonus actions). Does the bugbear's reach reset to 5ft for an instant between attacks, or should it be regarded as 10ft for the entire sequence?
Why does it matter?
As an example, consider a bugbear with multiple attacks and the grappler feat, which gives it advantage against a grappled opponent.
Now, if a bugbear grapples at 10ft range, it's normally pointless: it can perform the grapple (which is a special attack), but once it's established the bugbear's reach reverts to 5ft, the enemy is no longer within reach, and the grapple ends immediately.
However, with multiple attacks and the grappler feat, it could potentially get advantage on attacks subsequent to the grapple, before the grapple is lost after the last attack. But this only works if the 10ft range is maintained during the sequence of attacks. If it reverts in between attacks, even for a moment, we're back to grapples ending the instant they're established.