The German army changed to the round nose bullet in 1918, apparently because there was concern that the truncated cone bullet could be considered a "dum-dum" bullet. I have not see any indication that feeding problems with the Luger pistol increased at that time.
I was under the impression that they began the switch over in 1914 and that almost all issued 9mm Luger ammo was round nosed by 1916.
Only reason I'd heard of it was when I tried to find out where some Cupro Nickel truncated cone 9mm ammo I picked up had come from. That and reading up on the Truncated Cone hollow nose bullets of the SuperVel ammo I used to use in my HiPower.
According to this source the change to the roundnose bullet was in 1915-1916, with truncated cone bullets still being used for the 9mm Luger cartridge by US cartridge manufacturers.
The Luger has always been prone to feed problems, in part because of the same grip angle that is praised for its ergonomics. After moving the recoil spring to the grip, Luger changed the grip angle from the almost 90 degree Borchardt in an effort to get more positive breechblock closure, but (no free lunch) that resulted in a sharp angle to the magazine and less than optimal cartridge positioning.
Good points, and no doubt why Browning style 9mm pistols have fewer problems when mag catches get a bit worn.
Probably the switch from a shouldered bottle neck 7.65 to the straight tapered 9X19 also contributed.