Almost all auto loading pistol of the Glock design are setup for full power factory loads. If I wanted to shoot reduced loads I would expect to replace the main spring to compensate for the reduction in recoil function.
Each main spring has some flexibility as to the handload it will like, so reducing a load by a small margin should still allow for reliable cycling function. Go beyond the limit and functioning problem will occur.
Everyone has their own reaction to recoil, I personally feel the Glock 21 with full loads presents very little recoil, probably a little more than a full size 1911, but the felt recoil (the perceived recoil) is less than a 1911.
Nonetheless, if the recoil bothers you, probably switching out the main spring and working up a reliable reduced load is an option. You will probably need to replace the sights for the slower moving bullet to adjust for POA/POI.
If you also use this Glock for home defense or carry defense, you could switch out the target spring before starting your shooting session, and switch it back to the factory spring after the shooting session, so the full power defense loads would cycle reliably. Switching the sights back and worth.....not so easy! However, some would not recommend shooting a lot of reduced loads in a defense pistol and then carrying heavy loads.......they would say shoot a similar power load as the defense ammo you use.
I use Unique powder and only load 230 grain bullets. A proper taper crimp is best. If you are not crimping or using a very shallow crimp, that could make a difference in the cycle function, if the load you tried, is on the edge of not being quite enough to assure reliable function.
As Kevin recommends......
~~ Use that in conjunction with a chamber gage, and you can kiss malfunctions and feed failures goodbye.
Best Regards......Eagle Six