I was listening to the Ask Historians podcast about the Byzantines and the commentator referred to the Seljuks as 'hordes of Turks' invading Anatolia. Perhaps I'm wrong, but for me the word horde has a distinctly negative connotation indicating a large number of disorganized and primitive individuals. According to Wikipedia, at the decisive battle between the Seljuks and Byzantines at Manzikret the Byzantine forces outnumbered the Seljuks 2 to 1 so the Seljuks hardly fit the dictionary definition of horde at least in that instance. In addition I've never seen word used to refer to a European army, for example I've never seen the crusades referred to as 'hordes of Christians' invading the Middle East. This leads me to believe the term seems slightly outdated if not outright Euro-centric and racist, akin to referring to hunter gathers as savages. But I'm completely open to being corrected.
By the way the Ask Historians podcast is awesome, and the specific episode I'm referring to is amazing. Just being nitpicky and annoying, sorry.
If something is "problematic" or no is a matter of subjective view. In this context, the word "horde" does not necessarily have the negative connotations you think of.
The word "horde" is used to refer to organisations of nomads. The most notable example is the "Golden Horde", a state established in what is not southern Russia by the mongols. I am not an expert on mongol language, but wiki says that the word "horde" probably comes from the mongolian word for tent.
As the Seljuks were asian horse-archer nomads, referring to them as a "horde" can be seen as highlighting the similiarities to the Mongols. In fact, many mongol armies included substantial parts of ethnically turkish people. In modern turkish, "ordu" means as much as "army" in english.
In the specific context of turkish nomadic armies, using the word "horde" therefore does not carry negative implications. It is just a word for the kind of military organisation used by these people.
"Crusader horde" does turn up in the Encyclopedia of Warfare, in reference to the Seljuk Turks firing arrows at the Crusader army and the pilgrims in the camp.
The phrase also turns up a few times in David Nicolle's The First Crusade 1096-99: Conquest of the Holy Land.
Note that both of these references are about the same army that wound up massacring Jerusalem, so the "barbarian" connotation might still be in play.