It happens in every edition, though some are more prone to it than others.
What do you do, as DM, when it is clear that a combat has become a slog.Maybe everyone's dice are cold, or maybe the terrain and numbers and types of enemies limit option. or maybe the characters are either out of big hit resources or trying to save them for a future encounter. Whatever the cause, the combat has turned into a boring slog of swings and misses and hit point attrition.
What do you do?
I am generally loathe to just hand wave a victory until it is completely clear the PCs have won, just because dice are swingy and players make strange decisions and in a resource management oriented game what happens in this combat can have a significant impact on what follows. But that said, there is a point when I just "call it" for the PCs. That point is usually later than I should have for all the reasons I just mentioned.