The clutch pedal uses a pin - that it's shaft then goes into that arm of the piston, the hole at the top of that arm is where that pin's shaft goes thru and there is a tiny push nut washer-thingy used as a stay, on the opposite side that the pin-shaft - is what the stay uses - to stay in.
**Whew** - sorry for the redundancy, but since I don't have your car in front of me to help you with this, I can only work with whats available.
You just may need to fix the Pin-to-Clutch-Arm the stay or pin itself may have gotten slack and so the stay-nut being loose, lets the pin move and the arm will shift - so it can "jam" behind the bracket and hold in place.
It may be your problem so it may not need a new plunger - just fix the pin and stay for it...

In the Above - the Push Nut is for 2013 and
EARLIER models they revised the Pin and Clip used on the ARM for USA models for 2014 and later...looks like this...

...AND...
They made changes to the mounting - how the MASTER is held fast to the firewall and to the bracket...
However, the Clutch slave cylinder - the one that rests in the cavity the Clutch and flywheel are in - it's mounted to center and surround the engines output shaft to input shaft of the transmission. It floats in a concentric ring - that is bolted to the bell housing on the Transmission side. If you look carefully - that slave cylinder has two arms - one for fluid uptake from the master back on the clutch pedal worked by your foot, that pumps the fluid from your foot into that ring-shaped piston.

The lower arm in the photo with a green arrow is the burp line which; by the way it is mounted, is the highest spot of the master cylinder so it is set up to allow air to be bled out of that piston.

Although probable, that "sticking" pedal can also be from the tines of the clutch assembly hanging up on the piston so it binds and cannot release the clutch until it's removed by forcing - either by engine restart or by free-play in a worn clutch assembly, shaking it loose.