Probably either too big of a sweat shield, though I don't know Safariland's line-up that well, especially their IWB holsters to know if the offer something like that, or the holster is riding too low in the pants. The latter is more likely, but it may need to be the case to keep the gun/holster from rolling over the belt if it rode too high. A problem with short barrel guns.
I don't know if it is an option for the Shield line-up, but some folks use a holster for a longer barreled version of the gun for more in the pants stability, such as a G19 holster for a G26, or a G17 holster for a G19 or G26.